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 A197530 #8 Jun 02 2025 04:58:34 %S A197530 1,9,56,1419,107655,23325250,14991391782,27504159228709, %T A197530 145843735771766573 %N A197530 Number of n X n 0..4 arrays with each element x equal to the number of its horizontal and vertical neighbors equal to 2,0,1,0,0 for x=0,1,2,3,4. %C A197530 Every 0 is next to 0 2's, every 1 is next to 1 0'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 A197530 Diagonal of A197537 %e A197530 Some solutions containing all values 0 to 4 for n=4 %e A197530 ..0..0..0..1....1..0..0..0....1..2..1..1....0..0..0..0....1..0..0..0 %e A197530 ..3..0..3..2....1..0..4..0....0..3..0..0....3..0..4..0....2..3..0..0 %e A197530 ..0..4..0..1....2..3..0..0....0..0..4..0....0..3..0..0....1..0..4..0 %e A197530 ..0..0..0..1....1..0..3..0....0..0..0..0....1..2..1..1....1..0..0..0 %K A197530 nonn %O A197530 1,2 %A A197530 _R. H. Hardin_ Oct 16 2011