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 A189838 #6 Sep 12 2015 11:00:25 %S A189838 1,2,4,16,36,128,672,4264,25044,173712,1318904,11069056,96808692, %T A189838 927478976,9435033872,103783608480,1195155968388 %N A189838 Number of ways to place n nonattacking composite pieces rook + rider[2,2] on an n X n chessboard. %C A189838 a(n) is also number of permutations p of 1,2,...,n satisfying |p(j+2k)-p(j)|<>2k for all j>=1, k>=1, j+2k<=n %H A189838 V. Kotesovec, <a href="https://oeis.org/wiki/User:Vaclav_Kotesovec">Number of ways of placing non-attacking queens, kings, bishops and knights</a> (in English and Czech) %H A189838 Wikipedia, <a href="http://en.wikipedia.org/wiki/Fairy_chess_piece">Fairy chess piece</a> %Y A189838 Cf. A110128, A000170 %K A189838 nonn,hard %O A189838 1,2 %A A189838 _Vaclav Kotesovec_, Apr 29 2011