OFFSET
1,3
COMMENTS
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
LINKS
Gord Palameta, Table of n, a(n) for n = 1..188
EXAMPLE
2^11 - 1 = 23*89, 23 = 2*1*11 + 1, therefore a(1) = 1.
PROG
(PARI) forprime (n=3, 101, v=2^n-1; if (!isprime(v), print1((factor(v)[, 1][1]-1)\(2*n)", ")))
CROSSREFS
KEYWORD
nonn
AUTHOR
Jon Perry, Feb 12 2003
EXTENSIONS
More terms from Michel Marcus, Mar 17 2014
STATUS
approved