Named after | James Pierpont |
---|---|
No. of known terms | Thousands |
Conjectured no. of terms | Infinite |
Subsequence of | Pierpont number |
First terms | 2, 3, 5, 7, 13, 17, 19, 37, 73, 97, 109, 163, 193, 257, 433, 487, 577, 769, 1153, 1297, 1459, 2593, 2917, 3457, 3889 |
Largest known term | 3×2^{16,408,818} + 1 |
OEIS index | A005109 |
A Pierpont prime is a prime number of the form
A Pierpont prime with v = 0 is of the form , and is therefore a Fermat prime (unless u = 0). If v is positive then u must also be positive (because would be an even number greater than 2 and therefore not prime), and therefore the non-Fermat Piermont primes all have the form 6k + 1, when k is a positive integer (except for 2, when u = v = 0).
The first few Pierpont primes are:
As of 2022^{[update]}, the largest known Pierpont prime is 3×2^{16408818} + 1, which has 4,939,547 decimal digits.^{[1]}
Are there infinitely many Pierpont primes?
Empirically, the Pierpont primes do not seem to be particularly rare or sparsely distributed; there are 42 Pierpont primes less than 10^{6}, 65 less than 10^{9}, 157 less than 10^{20}, and 795 less than 10^{100}. There are few restrictions from algebraic factorisations on the Pierpont primes, so there are no requirements like the Mersenne prime condition that the exponent must be prime. Thus, it is expected that among n-digit numbers of the correct form , the fraction of these that are prime should be proportional to 1/n, a similar proportion as the proportion of prime numbers among all n-digit numbers. As there are numbers of the correct form in this range, there should be Pierpont primes.
Andrew M. Gleason made this reasoning explicit, conjecturing there are infinitely many Pierpont primes, and more specifically that there should be approximately 9n Pierpont primes up to 10^{n}.^{[2]} According to Gleason's conjecture there are Pierpont primes smaller than N, as opposed to the smaller conjectural number of Mersenne primes in that range.
When , the primality of can be tested by Proth's theorem. On the other hand, when alternative primality tests for are possible based on the factorization of as a small even number multiplied by a large power of 3.^{[3]}
In the mathematics of paper folding, the Huzita axioms define six of the seven types of fold possible. It has been shown that these folds are sufficient to allow the construction of the points that solve any cubic equation.^{[4]} It follows that they allow any regular polygon of N sides to be formed, as long as N ≥ 3 and is of the form 2^{m}3^{n}ρ, where ρ is a product of distinct Pierpont primes. This is the same class of regular polygons as those that can be constructed with a compass, straightedge, and angle-trisector.^{[2]} Regular polygons which can be constructed with only compass and straightedge (constructible polygons) are the special case where n = 0 and ρ is a product of distinct Fermat primes, themselves a subset of Pierpont primes.
In 1895, James Pierpont studied the same class of regular polygons; his work is what gives the name to the Pierpont primes. Pierpont generalized compass and straightedge constructions in a different way, by adding the ability to draw conic sections whose coefficients come from previously constructed points. As he showed, the regular N-gons that can be constructed with these operations are the ones such that the totient of N is 3-smooth. Since the totient of a prime is formed by subtracting one from it, the primes N for which Pierpont's construction works are exactly the Pierpont primes. However, Pierpont did not describe the form of the composite numbers with 3-smooth totients.^{[5]} As Gleason later showed, these numbers are exactly the ones of the form 2^{m}3^{n}ρ given above.^{[2]}
The smallest prime that is not a Pierpont (or Fermat) prime is 11; therefore, the hendecagon is the first regular polygon that cannot be constructed with compass, straightedge and angle trisector (or origami, or conic sections). All other regular N-gons with 3 ≤ N ≤ 21 can be constructed with compass, straightedge and trisector.^{[2]}
A Pierpont prime of the second kind is a prime number of the form 2^{u}3^{v} − 1. These numbers are
The largest known primes of this type are Mersenne primes; currently the largest known is (24,862,048 decimal digits). The largest known Pierpont prime of the second kind that is not a Mersenne prime is .^{[6]}
A generalized Pierpont prime is a prime of the form with k fixed primes p_{1} < p_{2} < p_{3} < ... < p_{k}. A generalized Pierpont prime of the second kind is a prime of the form with k fixed primes p_{1} < p_{2} < p_{3} < ... < p_{k}. Since all primes greater than 2 are odd, in both kinds p_{1} must be 2. The sequences of such primes in the OEIS are:
{p_{1}, p_{2}, p_{3}, ..., p_{k}} | + 1 | − 1 |
{2} | OEIS: A092506 | OEIS: A000668 |
{2, 3} | OEIS: A005109 | OEIS: A005105 |
{2, 5} | OEIS: A077497 | OEIS: A077313 |
{2, 3, 5} | OEIS: A002200 | OEIS: A293194 |
{2, 7} | OEIS: A077498 | OEIS: A077314 |
{2, 3, 5, 7} | OEIS: A174144 | OEIS: A347977 |
{2, 11} | OEIS: A077499 | OEIS: A077315 |
{2, 13} | OEIS: A173236 | OEIS: A173062 |