This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A165623 #3 Mar 31 2012 12:38:27
%S A165623 2,1,1,4,256,4194304,4503599627370496,
%T A165623 20769187434139310514121985316880384,
%U A165623 1766847064778384329583297500742918515827483896875618958121606201292619776
%N A165623 Integers of the form a(n)=2^n/n^2.
%e A165623 2^8/8^2=4, .. n :: 1,2,4,8,16,32,64,128,256,512,..
%t A165623 lst={};Do[i=2^n/n^2;If[IntegerQ[i],AppendTo[lst,i]],{n,6!}];lst
%o A165623 (PARI) a(n)=2^(2^(n-1))/(2^(2*n-2))
%Y A165623 Cf. A007758
%K A165623 nonn,easy
%O A165623 1,1
%A A165623 _Vladimir Joseph Stephan Orlovsky_, Sep 22 2009
%E A165623 Program by _Charles R Greathouse IV_, Oct 12 2009