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%I #16 Sep 29 2018 06:10:07
%S 1,1,4,3,163,5,25,60,1525,1445580,1609,3,17,1,59,36793758459,12379533,
%T 3421967,15,1,116905896337578232,20236572837,290792847537859675,60,
%U 2713800,461,7033,2112,1,120,1,35807,19,413328944,36,41
%N k such that 2kp+1 is the first factor of a nonprime Mersenne number M(p) = 2^p - 1.
%C 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 Gord Palameta, <a href="/A079324/b079324.txt">Table of n, a(n) for n = 1..188</a>
%e 2^11 - 1 = 23*89, 23 = 2*1*11 + 1, therefore a(1) = 1.
%o (PARI) forprime (n=3,101,v=2^n-1; if (!isprime(v),print1((factor(v)[,1][1]-1)\(2*n)",")))
%Y Cf. A054723.
%K nonn
%O 1,3
%A _Jon Perry_, Feb 12 2003
%E More terms from _Michel Marcus_, Mar 17 2014
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