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 A133511 #5 Mar 30 2012 18:51:53 %S A133511 0,0,-1,1,2,5,7,14,27,57,114,229,455,910,1819,3641,7282,14565,29127, %T A133511 58254,116507,233017,466034,932069,1864135,3728270,7456539,14913081, %U A133511 29826162,59652325,119304647,238609294,477218587,954437177,1908874354,3817748709,7635497415 %N A133511 a(n) = 3 A113405(n)- A113405(n+1). %F A133511 2a(n)-a(n+1)=A133513(n). %F A133511 A113405(n)-a(n)=A131531(n). %F A133511 O.g.f.: x^2(3x-1)/((1-2x)(1+x)(1-x+x^2)). - _R. J. Mathar_, Jul 22 2008 %F A133511 a(n+2)=4*(2^n-(-1)^n)/9+A117373(n+2)/3. [From _R. J. Mathar_, Jul 20 2009] %K A133511 sign %O A133511 0,5 %A A133511 _Paul Curtz_, Nov 30 2007 %E A133511 Edited and extended by _R. J. Mathar_, Jul 22 2008