1,1

2 together with the Fermat primes A019434.

Obviously if 2^n + 1 is a prime then either n = 0 or n is a power of 2. - njas, Apr 07 2004.

Eric Weisstein's World of Mathematics, Fermat Prime

A019434 is the main entry for these numbers.

Sequence in context: A072858 A087911 A099936 this_sequence A127063 A127837 A004249

Adjacent sequences: A092503 A092504 A092505 this_sequence A092507 A092508 A092509

nonn

Jorge Coveiro (jorgecoveiro(AT)yahoo.com), Apr 05 2004