A165623 - OEIS

%I #3 Mar 31 2012 12:38:27

%S 2,1,1,4,256,4194304,4503599627370496,

%T 20769187434139310514121985316880384,

%U 1766847064778384329583297500742918515827483896875618958121606201292619776

%N Integers of the form a(n)=2^n/n^2.

%e 2^8/8^2=4, .. n :: 1,2,4,8,16,32,64,128,256,512,..

%t lst={};Do[i=2^n/n^2;If[IntegerQ[i],AppendTo[lst,i]],{n,6!}];lst

%o (PARI) a(n)=2^(2^(n-1))/(2^(2*n-2))

%Y Cf. A007758

%K nonn,easy

%O 1,1

%A _Vladimir Joseph Stephan Orlovsky_, Sep 22 2009

%E Program by _Charles R Greathouse IV_, Oct 12 2009