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 A051759 #16 Oct 01 2021 19:07:05 %S A051759 1,2,4,31,307,2,9,755 %N A051759 Consider the problem of placing A051756(n) queens on an n X n board so that each queen attacks precisely 3 others. Sequence gives number of solutions up to square symmetry. %C A051759 A051569 (taken from the Martin Gardner references) is another version of this sequence. - _N. J. A. Sloane_, May 22 2014 %D A051759 M. Gardner, The Last Recreations, Springer, 1997, p. 282. %D A051759 M. Gardner, The Colossal Book of Mathematics, 2001, p. 209. %H A051759 Erich Friedman, <a href="/A051759/a051759.gif">Illustration of initial terms</a> %H A051759 Sean A. Irvine, <a href="https://github.com/archmageirvine/joeis/blob/master/src/irvine/oeis/a051/A051759.java">Java program</a> (github) %Y A051759 Cf. A051754-A051758, A051567-A051571, A019654. %K A051759 nonn,nice,more %O A051759 2,2 %A A051759 Robert Trent (trentrd(AT)hotmail.com), Aug 23 2000 %E A051759 a(8)-a(9) from _Sean A. Irvine_, Oct 01 2021