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 A120781 #2 Mar 31 2012 13:20:12 %S A120781 1,8,32,512,2048,16384,65536,2097152,8388608,67108864,268435456, %T A120781 4294967296,17179869184,137438953472,549755813888,35184372088832, %U A120781 140737488355328,1125899906842624,4503599627370496,72057594037927936 %N A120781 Denominators of partial sums of Catalan numbers scaled by powers of 1/8. %C A120781 Numerators are given under A120780. %C A120781 The listed numbers coincide with denominators of sum(C(k)/(-8)^k,k=0..n). For the numerators see A120789. In general these denominators may be different. See e.g. A120783 versus A120793 and A120787 versus A120796. %F A120781 a(n)=denominator(r(n)), with the rationals r(n):=sum(C(k)/8^k,k=0..n) with C(k):=A000108(k) (Catalan numbers). %K A120781 nonn,easy,frac %O A120781 0,2 %A A120781 _Wolfdieter Lang_, Jul 20 2006