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 A077580 #4 May 11 2007 03:00:00 %S A077580 1,3,4,7,6,17,8,15,13,23,12,35,14,31,28,31,18,53,20,49,37,47,24,71,31 %N A077580 Duplicate of A069213. %K A077580 dead %O A077580 1,2