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 A089409 #5 Aug 20 2017 23:16:18 %S A089409 1,1,2,4,5,11,11,17,22,24,36 %N A089409 Even-indexed terms of A089413. %K A089409 nonn %O A089409 0,3 %A A089409 _Antti Karttunen_, Nov 29 2003