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 A143892 #18 Nov 25 2018 13:44:34 %S A143892 1,2,1,5,6,29,47,300,665,5276,15554,160307,632041,8448701,44021226 %N A143892 Number of ways of placing kings with no more than 4 mutual attacks on an n X n chessboard symmetric under 90-degree rotation. %e A143892 Example: for n=3 the a(3)=5 solutions are %e A143892 . . . . . . K . K K . K . K . %e A143892 . . . . K . . . . . K . K . K %e A143892 . . . . . . K . K K . K . K . %Y A143892 Cf. A143870, A143875, A143881, A143886. %Y A143892 Cf. A143886, A143887, A143888, A143889, A143890, A143891, A143893. %K A143892 nonn,more,hard %O A143892 0,2 %A A143892 _R. H. Hardin_, Sep 04 2008