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 A189841 #6 Sep 12 2015 11:00:25 %S A189841 1,2,6,24,120,672,4128,28992,231936,2088960,20017152,207208704, %T A189841 2326900992,28338241536,373152276480,5206300028928 %N A189841 Number of ways to place n nonattacking composite pieces rook + rider[5,5] on an n X n chessboard. %C A189841 a(n) is also number of permutations p of 1,2,...,n satisfying |p(j+5k)-p(j)|<>5k for all j>=1, k>=1, j+5k<=n %H A189841 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 A189841 Wikipedia, <a href="http://en.wikipedia.org/wiki/Fairy_chess_piece">Fairy chess piece</a> %Y A189841 Cf. A189256, A000170, A189838, A189839, A189840 %K A189841 nonn,hard %O A189841 1,2 %A A189841 _Vaclav Kotesovec_, Apr 29 2011