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 A302421 #6 Sep 16 2020 18:55:34 %S A302421 1,3,11,42,372,4231,48037,1171867,30957683,1262711362,67345167687, %T A302421 6258369400424 %N A302421 Number of n X n 0..1 arrays with every element equal to 0, 1, 3 or 5 horizontally, diagonally or antidiagonally adjacent elements, with upper left element zero. %C A302421 Diagonal of A302427. %e A302421 Some solutions for n=5 %e A302421 ..0..1..0..1..0. .0..0..0..1..0. .0..0..0..0..1. .0..1..0..1..0 %e A302421 ..0..1..0..1..1. .0..1..1..1..0. .0..1..1..0..1. .1..1..0..1..0 %e A302421 ..0..1..0..1..0. .0..1..0..1..0. .0..1..0..1..0. .0..1..0..1..0 %e A302421 ..1..0..0..1..0. .0..0..0..1..0. .0..1..0..1..1. .1..0..1..1..0 %e A302421 ..1..0..1..0..0. .1..1..0..1..0. .0..1..0..1..0. .1..0..0..0..0 %Y A302421 Cf. A302427. %K A302421 nonn %O A302421 1,2 %A A302421 _R. H. Hardin_, Apr 07 2018