1,1

Mersenne numbers (with exception first one) are congruent to 7 or 31 mod 5!. This sequences is subset of A000043.

Is this 2 together with the terms of A112634? [From R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Mar 18 2009]

C. K. Caldwell, The largest known primes. [From R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Jul 31 2009]

p = {2, 3, 5, 7, 13, 17, 19, 31, 61, 89, 107, 127, 521, 607, 1279, 2203, 2281, 3217, 4253, 4423, 9689, 9941, 11213, 19937, 21701, 23209, 44497, 86243, 110503, 132049, 216091, 756839, 859433, 1257787, 1398269, 2976221, 3021377, 6972593, 13466917, 20996011, 24036583, 25964951, 30402457, 32582657, 37156667, 43112609}; a = {}; Do[If[Mod[2^p[[n]] - 1, 5! ] == 31, AppendTo[a, p[[n]]]], {n, 1, Length[p]}]; a (*Artur Jasinski*)

A000043, A000668, A124477, A139484, A145038, A145039, A145041, A145042

Sequence in context: A120130 A087484 A019382 this_sequence A125146 A051900 A120062

Adjacent sequences: A145037 A145038 A145039 this_sequence A145041 A145042 A145043

nonn

Artur Jasinski (grafix(AT)csl.pl), Sep 30 2008

42643801 inserted by R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Jul 31 2009