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 A297218 #7 Apr 19 2020 23:54:46 %S A297218 1,4,24,207,5570,261939,20599895,3819208252,1400212345305, %T A297218 937962844219314,1312275096984570369,3708386833907642906568, %U A297218 20177474743877943669370721,220442917573207336661039688056 %N A297218 Number of n X n 0..1 arrays with every 1 horizontally or antidiagonally adjacent to 1 neighboring 1's. %C A297218 Diagonal of A297224. %H A297218 R. H. Hardin, <a href="/A297218/b297218.txt">Table of n, a(n) for n = 1..23</a> %e A297218 Some solutions for n=5 %e A297218 ..1..1..0..0..0. .0..0..1..1..0. .1..1..0..0..0. .0..1..1..0..0 %e A297218 ..0..0..0..0..0. .0..0..0..1..1. .0..1..1..0..0. .0..0..0..1..1 %e A297218 ..0..1..1..0..0. .1..1..0..0..0. .0..0..1..1..0. .0..0..0..0..0 %e A297218 ..0..0..0..1..1. .0..0..0..1..1. .0..0..0..1..1. .0..0..1..0..1 %e A297218 ..0..0..0..0..0. .1..1..0..0..0. .1..1..0..0..0. .0..1..0..1..0 %Y A297218 Cf. A297224. %K A297218 nonn %O A297218 1,2 %A A297218 _R. H. Hardin_, Dec 27 2017