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A square has even multiplicity for all prime factors (it is of the form a 2 for some a). The first: 1, 4, 9, 16, 25, 36, 49, 64, 81, 100, 121, 144 (sequence A000290 in the OEIS). A cube has all multiplicities divisible by 3 (it is of the form a 3 for some a). The first: 1, 8, 27, 64, 125, 216, 343, 512, 729, 1000, 1331, 1728 (sequence A000578 ...
The primes of the form 2n+1 are the odd primes, including all primes other than 2. Some sequences have alternate names: 4n+1 are Pythagorean primes, 4n+3 are the integer Gaussian primes, and 6n+5 are the Eisenstein primes (with 2 omitted).
However, in this case, there is some fortuitous cancellation between the two factors of P n modulo 25, resulting in P 4k −1 ≡ 3 (mod 25). Combined with the fact that P 4 k −1 is a multiple of 8 whenever k > 1 , we have P 4 k −1 ≡ 128 (mod 200) and ends in 128, 328, 528, 728 or 928.
Name First elements Short description OEIS Mersenne prime exponents : 2, 3, 5, 7, 13, 17, 19, 31, 61, 89, ... Primes p such that 2 p − 1 is prime.: A000043 ...
If 2 k + 1 is prime and k > 0, then k itself must be a power of 2, [1] so 2 k + 1 is a Fermat number; such primes are called Fermat primes. As of 2023 [update] , the only known Fermat primes are F 0 = 3 , F 1 = 5 , F 2 = 17 , F 3 = 257 , and F 4 = 65537 (sequence A019434 in the OEIS ).
In number theory, an n-smooth (or n-friable) number is an integer whose prime factors are all less than or equal to n. [1] [2] For example, a 7-smooth number is a number in which every prime factor is at most 7. Therefore, 49 = 7 2 and 15750 = 2 × 3 2 × 5 3 × 7 are both 7-smooth, while 11 and 702 = 2 × 3 3 × 13 are not 7-smooth.
For Mersenne numbers, the trivial factors are not possible for prime n, so all factors are of the form 2kn + 1. In general, all factors of (b n − 1) /(b − 1) are of the form 2kn + 1, where b ≥ 2 and n is prime, except when n divides b − 1, in which case (b n − 1)/(b − 1) is divisible by n itself. Cunningham numbers of the form b n ...
Henryk Iwaniec showed that there are infinitely many numbers of the form + with at most two prime factors. [ 26 ] [ 27 ] Ankeny [ 28 ] and Kubilius [ 29 ] proved that, assuming the extended Riemann hypothesis for L -functions on Hecke characters , there are infinitely many primes of the form p = x 2 + y 2 {\displaystyle p=x^{2}+y^{2}} with y ...