This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A079324 #18 Aug 07 2025 16:55:02 %S A079324 1,1,4,3,163,5,25,60,1525,1445580,1609,3,17,1,59,36793758459,12379533, %T A079324 3421967,15,1,116905896337578232,20236572837,290792847537859675,60, %U A079324 2713800,461,7033,2112,1,120,1,35807,19,413328944,36,41,59441263078804,3284,3,1,45644 %N A079324 k such that 2kp+1 is the first factor of a nonprime Mersenne number M(p) = 2^p - 1. %C A079324 a(188) = 216 = k = (f-1)/2p for p=1231, f=531793. Although Mersenne numbers with p = 1213, 1217, 1229, 1231 are not fully factored, we know their smallest factors. One factor is known for p=1237 but it is not certain that it is the smallest. - _Gord Palameta_, Sep 26 2018 %H A079324 Gord Palameta, <a href="/A079324/b079324.txt">Table of n, a(n) for n = 1..188</a> %e A079324 2^11 - 1 = 23*89, 23 = 2*1*11 + 1, therefore a(1) = 1. %o A079324 (PARI) forprime (n=3,101,v=2^n-1; if (!isprime(v),print1((factor(v)[,1][1]-1)\(2*n)","))) %Y A079324 Cf. A054723. %K A079324 nonn %O A079324 1,3 %A A079324 _Jon Perry_, Feb 12 2003 %E A079324 More terms from _Michel Marcus_, Mar 17 2014