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 A051567 #26 Oct 27 2019 21:31:38 %S A051567 0,5,0,2,149,49,1,12897,2238 %N A051567 Consider problem of placing N queens on an n X n board so that each queen attacks precisely k others. Here k=1 and sequence gives number of inequivalent solutions when N is equal to the upper bound 2*floor(2n/3). %C A051567 a(n) = 0 if N does not achieve 2*floor(2n/3). %D A051567 M. Gardner, The Last Recreations, Springer, 1997, p. 282. %D A051567 M. Gardner, The Colossal Book of Mathematics, 2001, p. 209. %H A051567 Martin Gardner, <a href="http://www.scribd.com/doc/207185086/Gardner-1997-the-Last-Recreations">The Last Recreations</a>, 1997 %H A051567 Vaclav Kotesovec, <a href="/A051567/a051567.jpg">The unique solution for chessboard 9 X 9</a> %H A051567 Manfred Scheucher, <a href="/A051567/a051567.c.txt">C Code</a> %Y A051567 Cf. A051568-A051571, A051754-A051759, A019654. %Y A051567 The number of solutions when N takes its maximal value is A051757. %K A051567 nonn,more,nice %O A051567 3,2 %A A051567 _N. J. A. Sloane_ %E A051567 Description corrected by and one more term from _Jud McCranie_, Aug 25 2001