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 A130717 #2 Mar 30 2012 18:51:51 %S A130717 0,1,-1,0,0,2,-3,1,0,3,-5,2,0,4,-7,3,0,5,-9,4,0,6,-11,5,0,7,-13,6,0,8, %T A130717 -15,7,0,9,-17,8,0,10,-19,9,0,11,-21,10,0,12,-23,11,0,13,-25,12,0,14, %U A130717 -27,13,0,15,-29,14,0,16,-31,15,0,17,-33,16,0,18,-35,17,0,19,-37,18,0,20,-39,19,0,21,-41,20 %N A130717 Second differences of A130845. %K A130717 sign %O A130717 0,6 %A A130717 _Paul Curtz_, Aug 16 2007