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 A221253 #6 Jun 02 2025 08:13:14 %S A221253 16,2500,488601,103489929,22466712321,4919350997521,1080371161000000, %T A221253 237502965724417600,52227958295629168900,11486303574511411132081, %U A221253 2526218624607638969433649,555604441977129578423379025 %N A221253 Number of nX6 arrays of occupancy after each element moves to some horizontal or antidiagonal neighbor, with no occupancy greater than 2. %C A221253 Column 6 of A221255 %H A221253 R. H. Hardin, <a href="/A221253/b221253.txt">Table of n, a(n) for n = 1..13</a> %e A221253 Some solutions for n=3 %e A221253 ..0..1..2..2..1..2....0..1..2..1..2..1....0..2..2..0..2..2....0..2..2..1..0..1 %e A221253 ..1..1..1..1..1..0....0..2..1..1..2..0....0..2..1..1..2..1....0..1..1..1..2..0 %e A221253 ..0..1..2..1..1..0....1..1..0..1..1..1....0..1..0..0..2..0....0..2..2..0..2..1 %K A221253 nonn %O A221253 1,1 %A A221253 _R. H. Hardin_ Jan 06 2013