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 A189850 #6 Sep 12 2015 11:00:25 %S A189850 1,2,6,8,24,126,316,1344,7782,33930,172430,1106754,6432236,45188572, %T A189850 372437930,2728674526,23648822368,233010291526,2083328647344 %N A189850 Number of ways to place n nonattacking composite pieces rook + rider[1,3] on an n X n chessboard. %C A189850 In fairy chess, the rider [1,3] is called a Camelrider. %C A189850 a(n) is also number of permutations p of 1,2,...,n satisfying |p(i+k)-p(i)|<>3k AND |p(j+3k)-p(j)|<>k for all i>=1, j>=1, k>=1, i+k<=n, j+3k<=n %H A189850 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 A189850 Wikipedia, <a href="http://en.wikipedia.org/wiki/Fairy_chess_piece">Fairy chess piece</a> %Y A189850 Cf. A000170, A189837 %K A189850 nonn,hard %O A189850 1,2 %A A189850 _Vaclav Kotesovec_, Apr 29 2011