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 A221203 #8 May 05 2021 10:00:07 %S A221203 0,289,212,427716,4984812,1026177156,30374196832,3043294206016, %T A221203 133567666236732,10038761087929924,525060302368983108, %U A221203 34891927404610766400,1974298747702764055248,124298442666315631470276 %N A221203 Number of 4 X n arrays of occupancy after each element moves to some horizontal, diagonal or antidiagonal neighbor, with no occupancy greater than 2. %C A221203 Row 4 of A221200. %H A221203 R. H. Hardin, <a href="/A221203/b221203.txt">Table of n, a(n) for n = 1..15</a> %e A221203 Some solutions for n=3 %e A221203 ..1..2..0....0..2..2....0..2..2....0..2..0....0..2..0....0..2..1....0..2..1 %e A221203 ..0..2..0....0..2..1....0..2..0....1..2..1....2..2..1....2..2..0....0..2..1 %e A221203 ..0..2..2....0..2..1....0..2..1....2..2..0....0..2..0....0..2..0....1..2..0 %e A221203 ..1..2..0....0..2..0....1..2..0....0..2..0....1..2..0....1..2..0....0..2..1 %Y A221203 Cf. A221200. %K A221203 nonn %O A221203 1,2 %A A221203 _R. H. Hardin_ Jan 04 2013