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 A203535 #8 Jan 24 2023 15:29:08 %S A203535 0,4,72,3364,1700580,3743237124,44312000955508,2752746090434507556, %T A203535 840982281825673724760300,1273642755637661083775996170564 %N A203535 Number of n X n 0..2 arrays with every element neighboring horizontally or vertically both a 0 and a 1. %C A203535 Diagonal of A203542. %e A203535 Some solutions for n=5 %e A203535 ..0..1..2..0..1....1..1..0..0..0....2..1..0..0..2....0..0..1..0..1 %e A203535 ..0..1..2..0..1....0..2..2..1..1....0..1..2..1..1....1..1..1..0..1 %e A203535 ..2..1..2..0..2....0..2..1..0..1....0..1..1..2..0....1..0..1..0..0 %e A203535 ..1..0..0..1..0....1..1..1..0..0....1..2..0..2..0....0..0..1..0..1 %e A203535 ..1..0..1..1..0....1..0..0..1..1....1..0..0..1..1....2..1..1..0..1 %Y A203535 Cf. A203542. %K A203535 nonn %O A203535 1,2 %A A203535 _R. H. Hardin_, Jan 02 2012