Invitation: celebrating 50 years of OEIS, 250000 sequences, and Sloane's 75th, there will be a conference at DIMACS, Rutgers, Oct 9-10 2014.
1,1
If p is a prime then p is in the sequence iff 2^p-1 is a composite number.
V. Shevelev, Overpsudoprimes, Mersenne Numbers and Wieferich Primes, http://arxiv.org/abs/0806.3412
Table of n, a(n) for n=1..7.
Cf. A141232, A137576, A005420, A049479.
Sequence in context: A139337 A231115 A040110 * A048136 A180054 A166713
Adjacent sequences: A140449 A140450 A140451 * A140453 A140454 A140455
nonn
Vladimir Shevelev, Jun 26 2008
approved