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 A221133 #7 Jun 02 2025 08:11:04 %S A221133 0,9,656,643204,4235650596,259039174953636 %N A221133 Number of n X n arrays of occupancy after each element moves to some horizontal or vertical neighbor, with no occupancy greater than 2. %C A221133 Diagonal of A221139 %e A221133 Some solutions for n=3 %e A221133 ..2..1..0....2..2..1....0..2..1....0..1..2....2..2..1....0..0..1....2..1..0 %e A221133 ..1..2..1....2..0..1....2..1..0....1..0..2....1..0..2....1..1..2....2..2..1 %e A221133 ..0..2..0....0..0..1....2..1..0....2..1..0....0..0..1....2..2..0....0..1..0 %K A221133 nonn %O A221133 1,2 %A A221133 _R. H. Hardin_ Jan 02 2013