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 A278686 #9 Dec 05 2016 05:10:40 %S A278686 0,0,0,27,4860,164423,2651890,25981150,180378380,971905679,4316504623, %T A278686 16457726539,55463445891,168782705327,471407278652,1223710587908, %U A278686 2982045310010 %N A278686 Number of non-equivalent ways to place 7 non-attacking ferses on an n X n board. %C A278686 A fers is a leaper [1, 1]. %C A278686 Rotations and reflections of placements are not counted. If they are to be counted, see A201248. %H A278686 Wikipedia, <a href="http://en.wikipedia.org/wiki/Fairy_chess_piece">Fairy chess piece</a> %e A278686 There are 27 non-equivalent ways to place 7 non-attacking ferses (X) on a 4 X 4 board, rotations and reflections being ignored, e.g., these two: %e A278686 XXXX X.XX %e A278686 .... .... %e A278686 XXX. X.X. %e A278686 .... X.X. %Y A278686 Cf. A201248, A232567 (2 ferses), A278682 (3 ferses), A278683 (4 ferses), A278684 (5 ferses), A278685 (6 ferses), A278687, A278688. %K A278686 nonn,more %O A278686 1,4 %A A278686 _Heinrich Ludwig_, Dec 02 2016