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 A197882 #8 Jun 02 2025 05:12:36 %S A197882 1,4,6,155,2730,129294,13253562,2512321052 %N A197882 Number of n X n 0..4 arrays with each element x equal to the number of its horizontal and vertical neighbors equal to 0,2,1,1,1 for x=0,1,2,3,4. %C A197882 Every 0 is next to 0 0's, every 1 is next to 1 2's, every 2 is next to 2 1's, every 3 is next to 3 1's, every 4 is next to 4 1's %C A197882 Diagonal of A197889 %e A197882 Some solutions containing all values 0 to 4 for n=4 %e A197882 ..1..0..2..1....1..0..2..1....1..3..1..2....2..1..3..1....1..3..1..2 %e A197882 ..2..1..1..3....2..1..1..3....2..1..4..1....1..4..1..2....2..1..4..1 %e A197882 ..2..1..4..1....2..1..4..1....2..1..1..3....3..1..1..2....0..1..1..0 %e A197882 ..1..3..1..2....1..0..1..2....1..0..2..1....1..2..0..1....1..2..2..1 %K A197882 nonn %O A197882 1,2 %A A197882 _R. H. Hardin_ Oct 19 2011