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 A249906 #20 Aug 13 2020 14:02:28 %S A249906 1,0,-1,3,2,5,9,13,89,485,4891 %N A249906 a(n) is the index of the first occurrence of n in A249905, or -1 if n does not occur. %C A249906 a(n) is the smallest number of Hamiltonian cycles up to direction which requires at least an n-vertex graph to realize. %H A249906 Erich Friedman, <a href="https://erich-friedman.github.io/mathmagic/0912.html">Math Magic</a> (September 2012) %K A249906 sign,hard,more %O A249906 1,4 %A A249906 _Jeremy Tan_, Nov 08 2014 %E A249906 a(10)-a(11) using data from _Johan de Ruiter_ added by _Jeremy Tan_, Nov 02 2018