OFFSET
1,1
COMMENTS
If p is a prime then p is in the sequence iff 2^p-1 is a composite number.
LINKS
V. Shevelev, Overpseudoprimes, Mersenne Numbers and Wieferich Primes, arXiv:0806.3412 [math.NT], 2008-2012.
PROG
(PARI) f(n) = my(t); sumdiv(2*n+1, d, eulerphi(d)/(t=znorder(Mod(2, d))))*t-t+1; \\ A137576
isopp(n) = (n>1) && !isprime(n) && (n == f((n-1)/2)); \\ A141232
isok(n) = {fordiv(2^n-1, d, if (isopp(d), return (1)); ); return (0); } \\ Michel Marcus, Dec 09 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
Vladimir Shevelev, Jun 26 2008
EXTENSIONS
More terms from Michel Marcus, Dec 09 2018
STATUS
approved