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 A218244 #14 Sep 12 2015 11:00:28 %S A218244 1,1,1,3,6,21,75,415,2621,21066,195485,2083543,24744474,323438322, %T A218244 4596672672,70440521310 %N A218244 Number of inequivalent (rotationally and reflectively distinct) ways to place n nonattacking empresses on n X n board. %C A218244 An empress moves like a rook and a knight. %H A218244 V. Kotesovec, <a href="https://oeis.org/wiki/User:Vaclav_Kotesovec">Non-attacking chess pieces</a> %e A218244 a(4) = 3: different ways to place 4 nonattacking empresses on a 4 X 4 board: %e A218244 Xooo Xooo oXoo %e A218244 oXoo oooX Xooo %e A218244 ooXo ooXo oooX %e A218244 oooX oXoo ooXo %Y A218244 Cf. A137774, A002562. %K A218244 nonn,more %O A218244 1,4 %A A218244 _Witold Dlugosz_, Oct 24 2012