A116213 - OEIS

%I #3 Mar 31 2012 13:20:26

%S 1,3,3855,

%T 450552876409790643671482431940419874915447411150352389258589821042463539455

%N (2^(2^(2^n))-1)/(2^(2^n)+1).

%C 2^n+1 divides 2^(2^n)-1 iff n is a power of 2.

%F a(n) = (2^(2^(2^n))-1)/(2^(2^n)+1). a(n) = A051179(2^n)/A000215(n).

%t Table[ (2^2^2^n - 1) / (2^2^n + 1), {n,0,3} ]

%Y Cf. A000215 = Fermat numbers: 2^(2^n)+1. Cf. A051179 = 2^(2^n)-1.

%K nonn

%O 0,2

%A _Alexander Adamchuk_, Apr 08 2007