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 A221250 #7 Jun 02 2025 08:12:54 %S A221250 0,4,30,58081,78633756,4919350997521,720107530988047980, %T A221250 2283974100099963226425600 %N A221250 Number of n X n arrays of occupancy after each element moves to some horizontal or antidiagonal neighbor, with no occupancy greater than 2. %C A221250 Diagonal of A221255 %e A221250 Some solutions for n=3 %e A221250 ..0..2..0....1..2..0....0..2..0....1..2..0....0..2..1....1..2..1....0..2..1 %e A221250 ..2..2..0....1..2..0....1..2..0....0..2..1....1..2..0....0..2..0....1..2..1 %e A221250 ..1..2..0....1..2..0....2..2..0....1..2..0....1..2..0....0..2..1....0..2..0 %K A221250 nonn %O A221250 1,2 %A A221250 _R. H. Hardin_ Jan 06 2013