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 A051569 #12 Mar 28 2015 11:49:22 %S A051569 1,2,4,31,304,2,9,755,39302 %N A051569 Consider the problem of placing N = A051756(n) queens on an n X n board so that each queen attacks precisely 3 others; a(n) gives the number of inequivalent solutions. %D A051569 M. Gardner, The Last Recreations, Springer, 1997, p. 282. %D A051569 M. Gardner, The Colossal Book of Mathematics, 2001, p. 209. %Y A051569 Cf. A051567-A051571, A051754-A051759, A019654. %K A051569 nonn,more %O A051569 2,2 %A A051569 _N. J. A. Sloane_ %E A051569 I am not certain this description is correct, nor how rigorous the results are. Probably this is an incorrect version of A051759.