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 A221197 #8 Mar 25 2022 18:21:49 %S A221197 4,196,9025,427716,20277009,961434049,45583531009,2161117565476, %T A221197 102456463038084,4857310924636921,230276948274214416, %U A221197 10917021188851445889,517556134069075087921,24536386370101531606209 %N A221197 Number of n X 4 arrays of occupancy after each element moves to some horizontal, diagonal or antidiagonal neighbor, with no occupancy greater than 2. %C A221197 Column 4 of A221200. %H A221197 R. H. Hardin, <a href="/A221197/b221197.txt">Table of n, a(n) for n = 1..25</a> %e A221197 Some solutions for n=3 %e A221197 ..0..0..1..1....0..2..2..0....2..2..0..0....0..2..2..1....0..0..2..0 %e A221197 ..2..2..0..1....0..1..2..1....1..0..1..2....2..0..0..1....1..2..2..0 %e A221197 ..1..2..2..0....0..1..2..1....0..1..2..1....1..2..1..0....0..2..1..2 %Y A221197 Cf. A221200. %K A221197 nonn %O A221197 1,1 %A A221197 _R. H. Hardin_, Jan 04 2013