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 A302157 #7 Apr 20 2020 00:05:32 %S A302157 1,3,7,29,140,635,2853,19993,75825,786161,2915241,49663915,152854596, %T A302157 4893607560,13149908952,764803558904,1748158857032,193883417013099, %U A302157 378301363005384,78801036106269590,130887347815375440 %N A302157 Number of n X n 0..1 arrays with every element equal to 0, 1 or 3 horizontally, diagonally or antidiagonally adjacent elements, with upper left element zero. %C A302157 Diagonal of A302163. %H A302157 R. H. Hardin, <a href="/A302157/b302157.txt">Table of n, a(n) for n = 1..22</a> %e A302157 Some solutions for n=5 %e A302157 ..0..1..0..1..0. .0..1..0..1..0. .0..1..0..0..1. .0..0..1..1..0 %e A302157 ..0..1..0..1..1. .1..1..0..1..0. .0..1..0..1..0. .0..1..0..1..0 %e A302157 ..0..1..0..1..0. .0..1..0..1..1. .1..1..0..1..0. .0..1..0..1..0 %e A302157 ..0..1..0..1..0. .0..1..0..1..0. .0..1..0..1..0. .0..1..0..1..1 %e A302157 ..0..1..0..0..1. .0..1..0..1..0. .0..1..0..0..1. .0..1..0..1..0 %Y A302157 Cf. A302163. %K A302157 nonn %O A302157 1,2 %A A302157 _R. H. Hardin_, Apr 02 2018