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 A189858 #8 Apr 21 2021 13:44:34 %S A189858 1,2,6,24,80,326,1566,9544,53696,347382,2566892,21907934,184868860, %T A189858 1704360992,17294597926,192725663600,2139133978996 %N A189858 Number of ways to place n nonattacking composite pieces rook + rider[3,4] on an n X n chessboard. %C A189858 a(n) is also number of permutations p of 1,2,...,n satisfying |p(i+3k)-p(i)|<>4k AND |p(j+4k)-p(j)|<>3k for all i>=1, j>=1, k>=1, i+3k<=n, j+4k<=n. %H A189858 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 A189858 Wikipedia, <a href="http://en.wikipedia.org/wiki/Fairy_chess_piece">Fairy chess piece</a> %Y A189858 Cf. A000170, A189851, A189855. %K A189858 nonn,hard %O A189858 1,2 %A A189858 _Vaclav Kotesovec_, Apr 29 2011