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 A197443 #8 Jun 02 2025 04:55:08 %S A197443 1,5,81,4837,1108699,982926107,3148323076125,37516007592943532, %T A197443 1657994465210882573048 %N A197443 Number of n X n 0..4 arrays with each element x equal to the number of its horizontal and vertical neighbors equal to 2,1,1,0,0 for x=0,1,2,3,4. %C A197443 Every 0 is next to 0 2's, every 1 is next to 1 1's, every 2 is next to 2 1's, every 3 is next to 3 0's, every 4 is next to 4 0's %C A197443 Diagonal of A197450 %e A197443 Some solutions containing all values 0 to 4 for n=4 %e A197443 ..0..3..0..0....2..1..1..0....0..1..1..2....0..0..3..0....2..1..1..0 %e A197443 ..1..0..4..0....1..0..0..3....0..0..0..1....0..4..0..1....1..0..0..3 %e A197443 ..1..0..0..3....1..0..4..0....0..4..0..1....0..0..0..1....1..0..4..0 %e A197443 ..2..1..1..0....0..0..0..0....0..0..3..0....0..1..1..2....0..3..0..0 %K A197443 nonn %O A197443 1,2 %A A197443 _R. H. Hardin_ Oct 15 2011