1,3

a(n) = 2^(A000040(n)-2) - 1 = 2^(A040976(n)) - 1 = (2^A000040(n)/4) - 1 = (A061286(n)/2) - 1.

a(4)=31 because the 4th prime number is 7 and 7-2=5 and 2^5=32 and 32-1=31.

Cf. A000040, A040976, A061286.

Sequence in context: A094711 A143564 A153028 this_sequence A139287 A139307 A134709

Adjacent sequences: A135627 A135628 A135629 this_sequence A135631 A135632 A135633

easy,nonn

Omar E. Pol (info(AT)polprimos.com), Mar 01 2008