Since the Renaissance, every century has seen the solution of more mathematical problems than the century before, yet many mathematical problems, both major and minor, still remain unsolved.^{[1]} These unsolved problems occur in multiple domains, including physics, computer science, algebra, analysis, combinatorics, algebraic, differential, discrete and Euclidean geometries, graph, group, model, number, set and Ramsey theories, dynamical systems, partial differential equations, and more. Some problems may belong to more than one discipline of mathematics and be studied using techniques from different areas. Prizes are often awarded for the solution to a long-standing problem, and lists of unsolved problems (such as the list of Millennium Prize Problems) receive considerable attention.

This article is a composite of notable unsolved problems derived from many sources, including but not limited to lists considered authoritative. It does not claim to be comprehensive, it may not always be quite up to date, and it includes problems which are considered by the mathematical community to be widely varying in both difficulty and centrality to the science as a whole.

Various mathematicians and organizations have published and promoted lists of unsolved mathematical problems. In some cases, the lists have been associated with prizes for the discoverers of solutions.

List | Number of problems | Number unresolved or incompletely resolved |
Proposed by | Proposed in |
---|---|---|---|---|

Hilbert's problems^{[2]} |
23 | 15 | David Hilbert | 1900 |

Landau's problems^{[3]} |
4 | 4 | Edmund Landau | 1912 |

Taniyama's problems^{[4]} |
36 | - | Yutaka Taniyama | 1955 |

Thurston's 24 questions^{[5]}^{[6]} |
24 | - | William Thurston | 1982 |

Smale's problems | 18 | 14 | Stephen Smale | 1998 |

Millennium Prize problems | 7 | 6^{[7]} |
Clay Mathematics Institute | 2000 |

Simon problems | 15 | <12^{[8]}^{[9]} |
Barry Simon | 2000 |

Unsolved Problems on Mathematics for the 21st Century^{[10]} |
22 | - | Jair Minoro Abe, Shotaro Tanaka | 2001 |

DARPA's math challenges^{[11]}^{[12]} |
23 | - | DARPA | 2007 |

Of the original seven Millennium Prize Problems set by the Clay Mathematics Institute in 2000, six have yet to be solved as of May, 2021:^{[7]}

- Birch and Swinnerton-Dyer conjecture
- Hodge conjecture
- Navier–Stokes existence and smoothness
- P versus NP
- Riemann hypothesis
- Yang–Mills existence and mass gap

The seventh problem, the Poincaré conjecture, has been solved;^{[13]} however, a generalization called the smooth four-dimensional Poincaré conjecture—that is, whether a four-dimensional topological sphere can have two or more inequivalent smooth structures—is still unsolved.^{[14]}

- The Dneister Notebook (
*Dnestrovskaya Tetrad*) collects several hundred unresolved problems in algebra, particularly ring theory and modulus theory.^{[15]} - The Erlagol Notebook (
*Erlagolskaya Tetrad*) collects unresolved problems in algebra and model theory.^{[16]}

- Birch–Tate conjecture
- Bombieri–Lang conjecture
- Crouzeix's conjecture
- Eilenberg–Ganea conjecture
- Farrell–Jones conjecture
- Bost conjecture
- Finite lattice representation problem
- Green's conjecture
- Grothendieck–Katz p-curvature conjecture
- Hadamard conjecture
- Hilbert's fifteenth problem
- Hilbert's sixteenth problem
- Homological conjectures in commutative algebra
- Jacobson's conjecture
- Kaplansky's conjectures
- Köthe conjecture
- Kummer–Vandiver conjecture
- Existence of perfect cuboids and associated cuboid conjectures
- Pierce–Birkhoff conjecture
- Rota's basis conjecture
- Sendov's conjecture
- Serre's conjecture II
- Serre's multiplicity conjectures
- Uniformity conjecture
- Wild problem: Classification of pairs of
*n*×*n*matrices under simultaneous conjugation and problems containing it such as a lot of classification problems - Zariski–Lipman conjecture
- Zauner's conjecture: existence of SIC-POVMs in all dimensions

- The four exponentials conjecture on the transcendence of at least one of four exponentials of combinations of irrationals
^{[17]} - Lehmer's conjecture on the Mahler measure of non-cyclotomic polynomials
^{[18]} - The Pompeiu problem on the topology of domains for which some nonzero function has integrals that vanish over every congruent copy
^{[19]} - Schanuel's conjecture on the transcendence degree of exponentials of linearly independent irrationals
^{[17]} - Vitushkin's conjecture
- Invariant subspace problem
- Kung–Traub conjecture
^{[20]}

- Are (the Euler–Mascheroni constant), π +
*e*, π −*e*, π*e*, π/*e*, π^{e}, π^{√2}, π^{π},*e*^{π2}, ln π, 2^{e},*e*^{e}, Catalan's constant, or Khinchin's constant; rational, algebraic irrational, or transcendental? What is the irrationality measure of each of these numbers?^{[21]}^{[22]}^{[23]}

- Regularity of solutions of Vlasov–Maxwell equations
- Regularity of solutions of Euler equations
- Convergence of Flint Hills series

- The 1/3–2/3 conjecture: does every finite partially ordered set that is not totally ordered contain two elements
*x*and*y*such that the probability that*x*appears before*y*in a random linear extension is between 1/3 and 2/3?^{[24]} - Problems in Latin squares - Open questions concerning Latin squares
- The lonely runner conjecture: if runners with pairwise distinct speeds run round a track of unit length, will every runner be "lonely" (that is, be at least a distance from each other runner) at some time?
^{[25]} - Frankl's union-closed sets conjecture: for any family of sets closed under sums there exists an element (of the underlying space) belonging to half or more of the sets
^{[26]}

- The values of the Ramsey numbers, particularly
- Finding a function to model n-step self-avoiding walks.
^{[27]} - The values of the Van der Waerden numbers
- The values of the Dedekind numbers for .
^{[28]} - Give a combinatorial interpretation of the Kronecker coefficients.
^{[29]}

- Arnold–Givental conjecture and Arnold conjecture – relating symplectic geometry to Morse theory
- Quantum chaos: Berry–Tabor conjecture
- Birkhoff conjecture: if a billiard table is strictly convex and integrable, is its boundary necessarily an ellipse?
^{[30]} - Collatz conjecture (3
*n*+ 1 conjecture) - Eremenko's conjecture that every component of the escaping set of an entire transcendental function is unbounded
- Furstenberg conjecture – Is every invariant and ergodic measure for the action on the circle either Lebesgue or atomic?
- Margulis conjecture – Measure classification for diagonalizable actions in higher-rank groups
- MLC conjecture – Is the Mandelbrot set locally connected?
- Many problems concerning an outer billiard, for example showing that outer billiards relative to almost every convex polygon have unbounded orbits.
- Painlevé conjecture
- Quantum unique ergodicity conjecture
^{[31]} - Weinstein conjecture – Does a regular compact contact type level set of a Hamiltonian on a symplectic manifold carry at least one periodic orbit of the Hamiltonian flow?

- Lyapunov function: Lyapunov's second method for stability – For what classes of ODEs, describing dynamical systems, does the Lyapunov’s second method formulated in the classical and canonically generalized forms define the necessary and sufficient conditions for the (asymptotical) stability of motion?
- Is every reversible cellular automaton in three or more dimensions locally reversible?
^{[32]}

- Sudoku:
- How many puzzles have exactly one solution?
^{[33]} - How many puzzles with exactly one solution are minimal?
^{[33]} - What is the maximum number of givens for a minimal puzzle?
^{[33]}

- How many puzzles have exactly one solution?
- Tic-tac-toe variants:
- Given a width of tic-tac-toe board, what is the smallest dimension such that X is guaranteed a winning strategy?
^{[34]}

- Given a width of tic-tac-toe board, what is the smallest dimension such that X is guaranteed a winning strategy?
- What is the Turing completeness status of all unique elementary cellular automata?

- Abundance conjecture
- Bass conjecture
- Deligne conjecture
- Dixmier conjecture
- Fröberg conjecture
- Fujita conjecture
- Hartshorne's conjectures
^{[35]} - The Jacobian conjecture
- Manin conjecture
- Maulik–Nekrasov–Okounkov–Pandharipande conjecture on an equivalence between Gromov–Witten theory and Donaldson–Thomas theory
^{[36]} - Nakai conjecture
- Section conjecture
- Standard conjectures on algebraic cycles
- Tate conjecture
- Virasoro conjecture
- Weight-monodromy conjecture
- Zariski multiplicity conjecture
^{[37]}

- Flip - Termination of flips
- Resolution of singularities in characteristic

- Borsuk's problem on upper and lower bounds for the number of smaller-diameter subsets needed to cover a bounded
*n*-dimensional set. - The covering problem of Rado: if the union of finitely many axis-parallel squares has unit area, how small can the largest area covered by a disjoint subset of squares be?
^{[38]} - The Erdős–Oler conjecture that when is a triangular number, packing circles in an equilateral triangle requires a triangle of the same size as packing circles
^{[39]} - The kissing number problem for dimensions other than 1, 2, 3, 4, 8 and 24
^{[40]} - Reinhardt's conjecture that the smoothed octagon has the lowest maximum packing density of all centrally-symmetric convex plane sets
^{[41]} - Sphere packing problems, including the density of the densest packing in dimensions other than 1, 2, 3, 8 and 24, and its asymptotic behavior for high dimensions.
- Square packing in a square: what is the asymptotic growth rate of wasted space?
^{[42]} - Ulam's packing conjecture about the identity of the worst-packing convex solid
^{[43]}

- The spherical Bernstein's problem, a possible generalization of the original Bernstein's problem
- Carathéodory conjecture
- Cartan–Hadamard conjecture: Can the classical isoperimetric inequality for subsets of Euclidean space be extended to spaces of nonpositive curvature, known as Cartan–Hadamard manifolds?
- Chern's conjecture (affine geometry)
- Chern's conjecture for hypersurfaces in spheres
- Closed curve problem: Find (explicit) necessary and sufficient conditions that determine when, given two periodic functions with the same period, the integral curve is closed.
^{[44]} - The filling area conjecture, that a hemisphere has the minimum area among shortcut-free surfaces in Euclidean space whose boundary forms a closed curve of given length
^{[45]} - The Hopf conjectures relating the curvature and Euler characteristic of higher-dimensional Riemannian manifolds
^{[46]} - Yau's conjecture
- Yau's conjecture on the first eigenvalue

- The Hadwiger conjecture on covering
*n*-dimensional convex bodies with at most 2^{n}smaller copies^{[47]} - Solving the happy ending problem for arbitrary
^{[48]} - Improving lower and upper bounds for the Heilbronn triangle problem.
- Kalai's 3
^{d}conjecture on the least possible number of faces of centrally symmetric polytopes.^{[49]} - The Kobon triangle problem on triangles in line arrangements
^{[50]} - The Kusner conjecture that at most points can be equidistant in spaces
^{[51]} - The McMullen problem on projectively transforming sets of points into convex position
^{[52]} - Opaque forest problem

- How many unit distances can be determined by a set of n points in the Euclidean plane?
^{[53]}

- Finding matching upper and lower bounds for
*k*-sets and halving lines^{[54]} - Tripod packing
^{[55]}

- The Atiyah conjecture on configurations
^{[56]} - Bellman's lost in a forest problem – find the shortest route that is guaranteed to reach the boundary of a given shape, starting at an unknown point of the shape with unknown orientation
^{[57]} - Danzer's problem and Conway's dead fly problem – do Danzer sets of bounded density or bounded separation exist?
^{[58]} - The einstein problem – does there exist a two-dimensional shape that forms the prototile for an aperiodic tiling, but not for any periodic tiling?
^{[59]} - Falconer's conjecture that sets of Hausdorff dimension greater than in must have a distance set of nonzero Lebesgue measure
^{[60]} - Inscribed square problem, also known as Toeplitz' conjecture – does every Jordan curve have an inscribed square?
^{[61]} - The Kakeya conjecture – do -dimensional sets that contain a unit line segment in every direction necessarily have Hausdorff dimension and Minkowski dimension equal to ?
^{[62]} - The Kelvin problem on minimum-surface-area partitions of space into equal-volume cells, and the optimality of the Weaire–Phelan structure as a solution to the Kelvin problem
^{[63]} - Lebesgue's universal covering problem on the minimum-area convex shape in the plane that can cover any shape of diameter one
^{[64]} - Mahler's conjecture on the product of the volumes of a centrally symmetric convex body and its polar.
^{[65]} - Moser's worm problem – what is the smallest area of a shape that can cover every unit-length curve in the plane?
^{[66]} - The moving sofa problem – what is the largest area of a shape that can be maneuvered through a unit-width L-shaped corridor?
^{[67]} - Shephard's problem (a.k.a. Dürer's conjecture) – does every convex polyhedron have a net, or simple edge-unfolding?
^{[68]}^{[69]} - The Thomson problem – what is the minimum energy configuration of mutually-repelling particles on a unit sphere?
^{[70]}

- Borromean rings — are there three unknotted space curves, not all three circles, which cannot be arranged to form this link?
^{[71]} - Dissection into orthoschemes – is it possible for simplices of every dimension?
^{[72]}

- Uniform 5-polytopes – find and classify the complete set of these shapes
^{[73]}

- Cereceda's conjecture on the diameter of the space of colorings of degenerate graphs
^{[74]} - The Erdős–Faber–Lovász conjecture on coloring unions of cliques
^{[75]} - The Gyárfás–Sumner conjecture on χ-boundedness of graphs with a forbidden induced tree
^{[76]} - The Hadwiger conjecture relating coloring to clique minors
^{[77]} - The Hadwiger–Nelson problem on the chromatic number of unit distance graphs
^{[78]} - Jaeger's Petersen-coloring conjecture that every bridgeless cubic graph has a cycle-continuous mapping to the Petersen graph
^{[79]} - The list coloring conjecture that, for every graph, the list chromatic index equals the chromatic index
^{[80]} - The total coloring conjecture of Behzad and Vizing that the total chromatic number is at most two plus the maximum degree
^{[81]}

- The Albertson conjecture that the crossing number can be lower-bounded by the crossing number of a complete graph with the same chromatic number
^{[82]} - The Blankenship–Oporowski conjecture on the book thickness of subdivisions
^{[83]} - Conway's thrackle conjecture
^{[84]} - Harborth's conjecture that every planar graph can be drawn with integer edge lengths
^{[85]} - Negami's conjecture on projective-plane embeddings of graphs with planar covers
^{[86]} - The strong Papadimitriou–Ratajczak conjecture that every polyhedral graph has a convex greedy embedding
^{[87]} - Turán's brick factory problem – Is there a drawing of any complete bipartite graph with fewer crossings than the number given by Zarankiewicz?
^{[88]}

- Universal point sets of subquadratic size for planar graphs
^{[89]}

- Barnette's conjecture that every cubic bipartite three-connected planar graph has a Hamiltonian cycle
^{[90]} - Chvátal's toughness conjecture, that there is a number t such that every t-tough graph is Hamiltonian
^{[91]} - The cycle double cover conjecture that every bridgeless graph has a family of cycles that includes each edge twice
^{[92]} - The Erdős–Gyárfás conjecture on cycles with power-of-two lengths in cubic graphs
^{[93]} - The linear arboricity conjecture on decomposing graphs into disjoint unions of paths according to their maximum degree
^{[94]} - The Lovász conjecture on Hamiltonian paths in symmetric graphs
^{[95]} - The Oberwolfach problem on which 2-regular graphs have the property that a complete graph on the same number of vertices can be decomposed into edge-disjoint copies of the given graph.
^{[96]} - Szymanski's conjecture

- Characterise (non-)word-representable planar graphs
^{[97]}^{[98]}^{[99]}^{[100]} - Characterise word-representable near-triangulations containing the complete graph
*K*_{4}(such a characterisation is known for*K*_{4}-free planar graphs^{[101]}) - Classify graphs with representation number 3, that is, graphs that can be represented using 3 copies of each letter, but cannot be represented using 2 copies of each letter
^{[102]} - Is the line graph of a non-word-representable graph always non-word-representable?
^{[97]}^{[98]}^{[99]}^{[100]} - Are there any graphs on
*n*vertices whose representation requires more than floor(*n*/2) copies of each letter?^{[97]}^{[98]}^{[99]}^{[100]} - Is it true that out of all bipartite graphs, crown graphs require longest word-representants?
^{[103]} - Characterise word-representable graphs in terms of (induced) forbidden subgraphs.
^{[97]}^{[98]}^{[99]}^{[100]} - Which (hard) problems on graphs can be translated to words representing them and solved on words (efficiently)?
^{[97]}^{[98]}^{[99]}^{[100]}

- Conway's 99-graph problem: does there exist a strongly regular graph with parameters (99,14,1,2)?
^{[104]} - The Erdős–Hajnal conjecture on large cliques or independent sets in graphs with a forbidden induced subgraph
^{[105]} - The GNRS conjecture on whether minor-closed graph families have embeddings with bounded distortion
^{[106]} - Graham's pebbling conjecture on the pebbling number of Cartesian products of graphs
^{[107]} - The implicit graph conjecture on the existence of implicit representations for slowly-growing hereditary families of graphs
^{[108]} - Jørgensen's conjecture that every 6-vertex-connected
*K*_{6}-minor-free graph is an apex graph^{[109]} - Meyniel's conjecture that cop number is
^{[110]} - The reconstruction conjecture and new digraph reconstruction conjecture on whether a graph is uniquely determined by its vertex-deleted subgraphs.
^{[111]}^{[112]} - The second neighborhood problem: does every oriented graph contain a vertex for which there are at least as many other vertices at distance two as at distance one?
^{[113]} - Do there exist infinitely many strongly regular geodetic graphs, or any strongly regular geodetic graphs that are not Moore graphs?
^{[114]} - Sumner's conjecture: does every -vertex tournament contain as a subgraph every -vertex oriented tree?
^{[115]} - Tutte's conjectures that every bridgeless graph has a nowhere-zero 5-flow and every Petersen-minor-free bridgeless graph has a nowhere-zero 4-flow
^{[116]} - Vizing's conjecture on the domination number of cartesian products of graphs
^{[117]} - Zarankiewicz problem

- Does a Moore graph with girth 5 and degree 57 exist?
^{[118]} - What is the largest possible pathwidth of an n-vertex cubic graph?
^{[119]}

- The Kourovka Notebook is a collection of unsolved problems in group theory, first published in 1965 and updated many times since.
^{[120]}

- Andrews–Curtis conjecture
- Guralnick–Thompson conjecture
^{[121]} - Herzog–Schönheim conjecture
- The inverse Galois problem: is every finite group the Galois group of a Galois extension of the rationals?
- Problems in loop theory and quasigroup theory consider generalizations of groups

- Is every group surjunctive?
- Is every finitely presented periodic group finite?
- Are there an infinite number of Leinster groups?
- For which positive integers
*m*,*n*is the free Burnside group B(*m*,*n*) finite? In particular, is B(2, 5) finite? - Does generalized moonshine exist?

- The Cherlin–Zilber conjecture: A simple group whose first-order theory is stable in is a simple algebraic group over an algebraically closed field.
- Generalized star height problem
- For which number fields does Hilbert's tenth problem hold?
- Kueker's conjecture
^{[122]} - The Main Gap conjecture, e.g. for uncountable first order theories, for AECs, and for -saturated models of a countable theory.
^{[123]} - Shelah's categoricity conjecture for : If a sentence is categorical above the Hanf number then it is categorical in all cardinals above the Hanf number.
^{[123]} - Shelah's eventual categoricity conjecture: For every cardinal there exists a cardinal such that if an AEC K with LS(K)<= is categorical in a cardinal above then it is categorical in all cardinals above .
^{[123]}^{[124]} - The stable field conjecture: every infinite field with a stable first-order theory is separably closed.
- The Stable Forking Conjecture for simple theories
^{[125]} - Tarski's exponential function problem
- The universality problem for C-free graphs: For which finite sets C of graphs does the class of C-free countable graphs have a universal member under strong embeddings?
^{[126]} - The universality spectrum problem: Is there a first-order theory whose universality spectrum is minimum?
^{[127]} - Vaught's conjecture

- Is the theory of the field of Laurent series over decidable? of the field of polynomials over ?
- (BMTO) Is the Borel monadic theory of the real order decidable? (MTWO) Is the monadic theory of well-ordering consistently decidable?
^{[128]} - Assume K is the class of models of a countable first order theory omitting countably many types. If K has a model of cardinality does it have a model of cardinality continuum?
^{[129]} - If the class of atomic models of a complete first order theory is categorical in the , is it categorical in every cardinal?
^{[130]}^{[131]} - Does there exist an o-minimal first order theory with a trans-exponential (rapid growth) function?
- Is there a logic L which satisfies both the Beth property and Δ-interpolation, is compact but does not satisfy the interpolation property?
^{[132]} - Is every infinite, minimal field of characteristic zero algebraically closed? (Here, "minimal" means that every definable subset of the structure is finite or co-finite.)
- Does a finitely presented homogeneous structure for a finite relational language have finitely many reducts?
- Do the Henson graphs have the finite model property?

- Determine the structure of Keisler's order
^{[133]}^{[134]}

Main page: Category:Unsolved problems in number theory |

- Beilinson conjecture
- Brocard's problem: existence of integers, (
*n*,*m*), such that*n*! + 1 =*m*^{2}other than*n*= 4, 5, 7 - Carmichael's totient function conjecture
- Casas-Alvero conjecture
- Catalan–Dickson conjecture on aliquot sequences
- Congruent number problem (a corollary to Birch and Swinnerton-Dyer conjecture, per Tunnell's theorem)
- Piltz divisor problem, especially Dirichlet's divisor problem
- Erdős–Moser problem: is 1
^{1}+ 2^{1}= 3^{1}the only solution to the Erdős–Moser equation? - Erdős–Straus conjecture
- Erdős–Ulam problem
- Van der Corput's method: Exponent pair conjecture
- Grand Riemann hypothesis
- Goormaghtigh conjecture
- Grimm's conjecture
- The Gauss circle problem – how far can the number of integer points in a circle centered at the origin be from the area of the circle?
- Hall's conjecture
- Hilbert's eleventh problem
- Hilbert's ninth problem
- Hilbert–Pólya conjecture
- Hilbert's twelfth problem
- Keating–Snaith conjecture concerning the asymptotics of an integral involving the Riemann zeta function
^{[135]} - Lehmer's totient problem: if φ(
*n*) divides*n*− 1, must*n*be prime? - Leopoldt's conjecture
- Lindelöf hypothesis and its consequence, the density hypothesis for zeroes of the Riemann zeta function (see Bombieri–Vinogradov theorem)
- Littlewood conjecture
- Montgomery's pair correlation conjecture
*n*conjecture- Newman's conjecture
- Pillai's conjecture
- Sato–Tate conjecture
- Scholz conjecture
- Singmaster's conjecture: is there a finite upper bound on the multiplicities of the entries greater than 1 in Pascal's triangle?
^{[136]} - Vojta's conjecture
- The uniqueness conjecture for Markov numbers
^{[137]}

- Do any odd perfect numbers exist?
- Are there infinitely many perfect numbers?
- Do quasiperfect numbers exist?
- Do any odd weird numbers exist?
- Do any Lychrel numbers exist?
- Is 10 a solitary number?
- Are there infinitely many amicable numbers?
- Are there any pairs of amicable numbers which have opposite parity?
- Are there any pairs of relatively prime amicable numbers?
- Are there infinitely many betrothed numbers?
- Are there any pairs of betrothed numbers which have same parity?
- Do any Taxicab(5, 2, n) exist for
*n*> 1? - Is π a normal number (its digits are "random")?
^{[138]} - Which integers can be written as the sum of three perfect cubes?
^{[139]} - Is there a covering system with odd distinct moduli?
^{[140]}

- Find the value of the De Bruijn–Newman constant

- Beal's conjecture
- Erdős conjecture on arithmetic progressions
- Erdős–Turán conjecture on additive bases
- Fermat–Catalan conjecture
- Gilbreath's conjecture
- Goldbach's conjecture
- Lander, Parkin, and Selfridge conjecture
- Lemoine's conjecture
- Minimum overlap problem
- Pollock octahedral numbers conjecture
- Skolem problem
- The values of
*g*(*k*) and*G*(*k*) in Waring's problem

- Do the Ulam numbers have a positive density?

- Determine growth rate of
*r*_{k}(*N*) (see Szemerédi's theorem)

- Are there infinitely many real quadratic number fields with unique factorization (Class number problem)?
- Greenberg's conjectures
- Hermite's problem
- Kummer–Vandiver conjecture
- Stark conjectures (including Brumer–Stark conjecture)

- Characterize all algebraic number fields that have some power basis.

- Integer factorization: Can integer factorization be done in polynomial time?

- Goldbach conjecture
- Twin prime conjecture
- Polignac's conjecture
- Brocard's conjecture
- Catalan's Mersenne conjecture
- Agoh–Giuga conjecture
- Dubner's conjecture
- The Gaussian moat problem: is it possible to find an infinite sequence of distinct Gaussian prime numbers such that the difference between consecutive numbers in the sequence is bounded?
- New Mersenne conjecture
- Erdős–Mollin–Walsh conjecture
- Bunyakovsky conjecture
- Dickson's conjecture
- Schinzel's hypothesis H
- Fortune's conjecture (that no Fortunate number is composite)
- Landau's problems
- Feit–Thompson conjecture
- Artin's conjecture on primitive roots
- Is 78,557 the lowest Sierpiński number (so-called Selfridge's conjecture)?
- Does the conjectural converse of Wolstenholme's theorem hold for all natural numbers?
- Elliott–Halberstam conjecture
- Problems associated to Linnik's theorem

- Are there infinitely many prime quadruplets?
- Are there infinitely many cousin primes?
- Are there infinitely many sexy primes?
- Are there infinitely many Mersenne primes (Lenstra–Pomerance–Wagstaff conjecture); equivalently, infinitely many even perfect numbers?
- Are there infinitely many Wagstaff primes?
- Are there infinitely many Sophie Germain primes?
- Are there infinitely many Pierpont primes?
- Are there infinitely many regular primes, and if so is their relative density ?
- For any given integer
*b*which is not a perfect power and not of the form −4*k*^{4}for integer*k*, are there infinitely many repunit primes to base*b*? - Are there infinitely many Cullen primes?
- Are there infinitely many Woodall primes?
- Are there infinitely many Carol primes?
- Are there infinitely many Kynea primes?
- Are there infinitely many palindromic primes to every base?
- Are there infinitely many Fibonacci primes?
- Are there infinitely many Lucas primes?
- Are there infinitely many Pell primes?
- Are there infinitely many Newman–Shanks–Williams primes?
- Are all Mersenne numbers of prime index square-free?
- Are there infinitely many Wieferich primes?
- Are there any Wieferich primes in base 47?
- Are there any composite
*c*satisfying 2^{c − 1}≡ 1 (mod*c*^{2})? - For any given integer
*a*> 0, are there infinitely many primes*p*such that*a*^{p − 1}≡ 1 (mod*p*^{2})?^{[141]} - Can a prime
*p*satisfy 2^{p − 1}≡ 1 (mod*p*^{2}) and 3^{p − 1}≡ 1 (mod*p*^{2}) simultaneously?^{[142]} - Are there infinitely many Wilson primes?
- Are there infinitely many Wolstenholme primes?
- Are there any Wall–Sun–Sun primes?
- For any given integer
*a*> 0, are there infinitely many Lucas–Wieferich primes associated with the pair (*a*, −1)? (Specially, when*a*= 1, this is the Fibonacci-Wieferich primes, and when*a*= 2, this is the Pell-Wieferich primes) - Is every Fermat number 2
^{2n}+ 1 composite for ? - Are all Fermat numbers square-free?
- For any given integer
*a*which is not a square and does not equal to −1, are there infinitely many primes with*a*as a primitive root? - Is 509,203 the lowest Riesel number?
- For any given integers
*k*≥ 1,*b*≥ 2,*c*≠ 0, with gcd(*k*,*c*) = 1 and gcd(*b*,*c*) = 1, are there infinitely many primes of the form (*k*×*b*^{n}+*c*)/gcd(*k*+*c*,*b*−1) with integer*n*≥ 1? - Does every prime number appear in the Euclid–Mullin sequence?
- Find the smallest Skewes' number

- The problem of finding the ultimate core model, one that contains all large cardinals.
- Woodin's Ω-conjecture.
- (Woodin) Does the Generalized Continuum Hypothesis below a strongly compact cardinal imply the Generalized Continuum Hypothesis everywhere?
- Does the Generalized Continuum Hypothesis entail for every singular cardinal ?
- Does the Generalized Continuum Hypothesis imply the existence of an ℵ
_{2}-Suslin tree? - If ℵ
_{ω}is a strong limit cardinal, then 2^{ℵω}< ℵ_{ω1}(see Singular cardinals hypothesis). The best bound, ℵ_{ω4}, was obtained by Shelah using his pcf theory.

- Does the consistency of the existence of a strongly compact cardinal imply the consistent existence of a supercompact cardinal?
- Does there exist a Jónsson algebra on ℵ
_{ω}? - Without assuming the axiom of choice, can a nontrivial elementary embedding
*V*→*V*exist? - Is OCA (Open coloring axiom) consistent with ?

- Connes embedding problem (Zhengfeng Ji, Anand Natarajan, Thomas Vidick, John Wright, Henry Yuen, 2020)

- Kadison–Singer problem (Adam Marcus, Daniel Spielman and Nikhil Srivastava, 2013)
^{[144]}^{[145]}(and the Feichtinger's conjecture, Anderson’s paving conjectures, Weaver’s discrepancy theoretic and conjectures, Bourgain-Tzafriri conjecture and -conjecture)

- Erdős sumset conjecture (Joel Moreira, Florian Richter, Donald Robertson, 2018)
^{[146]} - McMullen's g-conjecture on the possible numbers of faces of different dimensions in a simplicial sphere (also Grünbaum conjecture, several conjectures of Kühnel) (Karim Adiprasito, 2018)
^{[147]}^{[148]} - Hirsch conjecture (Francisco Santos Leal, 2010)
^{[149]}^{[150]}

- The angel problem (Various independent proofs, 2006)
^{[151]}^{[152]}^{[153]}^{[154]}

- Yau's conjecture (Antoine Song, 2018)
^{[155]} - Pentagonal tiling (Michaël Rao, 2017)
^{[156]} - Erdős distinct distances problem (Larry Guth, Netz Hawk Katz, 2011)
^{[157]} - Heterogeneous tiling conjecture (squaring the plane) (Frederick V. Henle and James M. Henle, 2008)
^{[158]} - Kepler conjecture (Ferguson, Hales, 1998)
^{[159]} - Dodecahedral conjecture (Hales, McLaughlin, 1998)
^{[160]}

- Ringel's conjecture on graceful labeling of trees (Richard Montgomery, Benny Sudakov, Alexey Pokrovskiy, 2020)
^{[161]}^{[162]} - Hedetniemi's conjecture on the chromatic number of tensor products of graphs (Yaroslav Shitov, 2019)
^{[163]} - Babai's problem (Problem 3.3 in "Spectra of Cayley graphs") (Alireza Abdollahi, Maysam Zallaghi, 2015)
^{[164]} - Alspach's conjecture (Darryn Bryant, Daniel Horsley, William Pettersson, 2014)
- Scheinerman's conjecture (Jeremie Chalopin and Daniel Gonçalves, 2009)
^{[165]} - Erdős–Menger conjecture (Aharoni, Berger 2007)
^{[166]} - Road coloring conjecture (Avraham Trahtman, 2007)
^{[167]}

- Hanna Neumann conjecture (Mineyev, 2011)
^{[168]} - Density theorem (Namazi, Souto, 2010)
^{[169]} - Full classification of finite simple groups (Harada, Solomon, 2008)

- Duffin-Schaeffer conjecture (Dimitris Koukoulopoulos, James Maynard, 2019)
- Main conjecture in Vinogradov's mean-value theorem (Jean Bourgain, Ciprian Demeter, Larry Guth, 2015)
^{[170]} - Goldbach's weak conjecture (Harald Helfgott, 2013)
^{[171]}^{[172]}^{[173]} - Serre's modularity conjecture (Chandrashekhar Khare and Jean-Pierre Wintenberger, 2008)
^{[174]}^{[175]}^{[176]} - Fermat's Last Theorem (Andrew Wiles and Richard Taylor, 1995)
^{[177]}^{[178]}

- Burr–Erdős conjecture (Choongbum Lee, 2017)
^{[179]} - Boolean Pythagorean triples problem (Marijn Heule, Oliver Kullmann, Victor Marek, 2016)
^{[180]}^{[181]}

- Deciding whether the Conway knot is a slice knot (Lisa Piccirillo, 2020)
^{[182]}^{[183]} - Virtual Haken conjecture (Agol, Groves, Manning, 2012)
^{[184]}(and by work of Wise also virtually fibered conjecture) - Hsiang–Lawson's conjecture (Brendle, 2012)
^{[185]} - Ehrenpreis conjecture (Kahn, Markovic, 2011)
^{[186]} - Atiyah conjecture (Austin, 2009)
^{[187]} - Cobordism hypothesis (Jacob Lurie, 2008)
^{[188]} - Geometrization conjecture, proven by Grigori Perelman
^{[189]}in a series of preprints in 2002–2003.^{[190]} - Spherical space form conjecture (Grigori Perelman, 2006)

- Erdős discrepancy problem (Terence Tao, 2015)
^{[191]} - Umbral moonshine conjecture (John F. R. Duncan, Michael J. Griffin, Ken Ono, 2015)
^{[192]} - Anderson conjecture (Cheeger, Naber, 2014)
^{[193]} - Gaussian correlation inequality (Thomas Royen, 2014)
^{[194]} - Willmore conjecture (Fernando Codá Marques and André Neves, 2012)
^{[195]} - Beck's 3-permutations conjecture (Newman, Nikolov, 2011)
^{[196]} - Bloch–Kato conjecture (Voevodsky, 2011)
^{[197]}(and Quillen–Lichtenbaum conjecture and by work of Geisser and Levine (2001) also Beilinson–Lichtenbaum conjecture^{[198]}^{[199]}^{[200]}) - Sidon set problem (J. Cilleruelo, I. Ruzsa and C. Vinuesa, 2010)
^{[201]} - Kauffman–Harary conjecture (Matmann, Solis, 2009)
^{[202]} - Surface subgroup conjecture (Kahn, Markovic, 2009)
^{[203]} - Normal scalar curvature conjecture and the Böttcher–Wenzel conjecture (Lu, 2007)
^{[204]} - Nirenberg–Treves conjecture (Nils Dencker, 2005)
^{[205]}^{[206]} - Lax conjecture (Lewis, Parrilo, Ramana, 2005)
^{[207]} - The Langlands–Shelstad fundamental lemma (Ngô Bảo Châu and Gérard Laumon, 2004)
^{[208]} - Tameness conjecture and Ahlfors measure conjecture (Ian Agol, 2004)
^{[209]} - Robertson–Seymour theorem (Robertson, Seymour, 2004)
^{[210]} - Stanley–Wilf conjecture (Gábor Tardos and Adam Marcus, 2004)
^{[211]}(and also Alon–Friedgut conjecture) - Green–Tao theorem (Ben J. Green and Terence Tao, 2004)
^{[212]} - Ending lamination theorem (Jeffrey F. Brock, Richard D. Canary, Yair N. Minsky, 2004)
^{[213]} - Carpenter's rule problem (Connelly, Demaine, Rote, 2003)
^{[214]} - Cameron–Erdős conjecture (Ben J. Green, 2003, Alexander Sapozhenko, 2003)
^{[215]}^{[216]} - Milnor conjecture (Vladimir Voevodsky, 2003)
^{[217]} - Kemnitz's conjecture (Reiher, 2003, di Fiore, 2003)
^{[218]} - Nagata's conjecture (Shestakov, Umirbaev, 2003)
^{[219]} - Kirillov's conjecture (Baruch, 2003)
^{[220]} - Poincaré conjecture (Grigori Perelman, 2002)
^{[189]} - Strong perfect graph conjecture (Maria Chudnovsky, Neil Robertson, Paul Seymour and Robin Thomas, 2002)
^{[221]} - Kouchnirenko’s conjecture (Haas, 2002)
^{[222]} - Vaught conjecture (Knight, 2002)
^{[223]} - Double bubble conjecture (Hutchings, Morgan, Ritoré, Ros, 2002)
^{[224]} - Catalan's conjecture (Preda Mihăilescu, 2002)
^{[225]} *n*! conjecture (Haiman, 2001)^{[226]}(and also Macdonald positivity conjecture)- Kato's conjecture (Auscher, Hofmann, Lacey, McIntosh and Tchamitchian, 2001)
^{[227]} - Deligne's conjecture on 1-motives (Luca Barbieri-Viale, Andreas Rosenschon, Morihiko Saito, 2001)
^{[228]} - Modularity theorem (Breuil, Conrad, Diamond and Taylor, 2001)
^{[229]} - Erdős–Stewart conjecture (Florian Luca, 2001)
^{[230]} - Berry–Robbins problem (Atiyah, 2000)
^{[231]} - Erdős–Graham problem (Croot, 2000)
^{[232]} - Honeycomb conjecture (Thomas Hales, 1999)
^{[233]} - Gradient conjecture (Krzysztof Kurdyka, Tadeusz Mostowski, Adam Parusinski, 1999)
^{[234]} - Bogomolov conjecture (Emmanuel Ullmo, 1998, Shou-Wu Zhang, 1998)
^{[235]}^{[236]} - Lafforgue's theorem (Laurent Lafforgue, 1998)
^{[237]} - Ganea conjecture (Iwase, 1997)
^{[238]} - Torsion conjecture (Merel, 1996)
^{[239]} - Harary's conjecture (Chen, 1996)
^{[240]}