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 A189854 #6 Sep 12 2015 11:00:25 %S A189854 1,2,6,12,36,174,500,2052,12112,65092,407882,2954798,20568796, %T A189854 157579774,1346294112,11580692142,110130002110,1145065547108 %N A189854 Number of ways to place n nonattacking composite pieces rook + rider[2,3] on an n X n chessboard. %C A189854 (in fairy chess the rider [2,3] is called a Zebrarider) %C A189854 a(n) is also number of permutations p of 1,2,...,n satisfying |p(i+2k)-p(i)|<>3k AND |p(j+3k)-p(j)|<>2k for all i>=1, j>=1, k>=1, i+2k<=n, j+3k<=n %H A189854 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 A189854 Wikipedia, <a href="http://en.wikipedia.org/wiki/Fairy_chess_piece">Fairy chess piece</a> %Y A189854 Cf. A000170, A189837, A189850 %K A189854 nonn,hard %O A189854 1,2 %A A189854 _Vaclav Kotesovec_, Apr 29 2011