43 (forty-three) is the natural number following 42 and preceding 44.
Forty-three is the 14th smallest prime number. The previous is forty-one, with which it comprises a twin prime, and the next is forty-seven. 43 is the smallest prime that is not a Chen prime. It is also the third Wagstaff prime.
43 is the fourth term of Sylvester's sequence, one more than the product of the previous terms (2 × 3 × 7).
43 is a centered heptagonal number.
Let a0 = a1 = 1, and thenceforth an = 1/n − 1(a02 + a12 + ... + an − 12). This sequence continues 1, 1, 2, 3, 5, 10, 28, 154... (sequence A003504 in the OEIS). a43 is the first term of this sequence that is not an integer.
43 is a Heegner number.
43 is the largest prime which divides the order of the Janko group J4.
43 is a repdigit in base 6 (111).
43 is the number of triangles inside the Sri Yantra.
43 is the largest natural number that is not an (original) McNugget number.
43 is the smallest prime number expressible as the sum of 2, 3, 4, or 5 different primes:
43 is the smallest number with the property 43 = 4*prime(3) + 3*prime(3). Where prime(n) is the n-th prime number. There are only two numbers with that property, the other one is 127.
When taking the first six terms of the Taylor series for computing e, one obtains
which is also five minus the fifth harmonic number.
Every solvable configuration of the Fifteen puzzle can be solved in no more than 43 multi-tile moves (i.e. when moving two or three tiles at once is counted as one move).
In auto racing:
In American football:
George H. W. Bush (Republican) [Bush 41—i.e., the first president Bush, George H. W. Bush was the forty-first President of the United States, and so some have referred to him in this way since the election of his son, George W. Bush or Bush 43—the forty-third president of the United States.]