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 A138878 #2 Mar 31 2012 12:38:14 %S A138878 0,1,7,262135 %N A138878 First differences of A049384. %K A138878 nonn %O A138878 1,3 %A A138878 _Vladimir Joseph Stephan Orlovsky_, May 16 2008