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 A229165 #18 Sep 27 2013 14:14:41 %S A229165 1,2,7,104,7255,2280064,2708080414,13039886441460 %N A229165 a(n) is the number of n X n matrices of 0's, 1's and -1's in which the entries in each row or column sum to 1 and there are no adjacent -1's or 1's in any row or column. %Y A229165 Cf. A005130 (Robbins numbers). %Y A229165 Cf. A050204 (entries in each row or column sum to 1). %K A229165 nonn,more %O A229165 1,2 %A A229165 _Eric W. Weisstein_, Sep 25 2013 %E A229165 Additional terms from _R. H. Hardin_, Sep 25 2013