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 A221258 #6 Jun 02 2025 08:13:44 %S A221258 0,64,112,58081,1319409,103489929,4085800416,226720727104, %T A221258 10445351809532,530909339760900,25591483232781872,1268920553028932644, %U A221258 61970903049203536750,3051063081822723807844,149565983362653741790314 %N A221258 Number of 4Xn arrays of occupancy after each element moves to some horizontal or antidiagonal neighbor, with no occupancy greater than 2. %C A221258 Row 4 of A221255 %H A221258 R. H. Hardin, <a href="/A221258/b221258.txt">Table of n, a(n) for n = 1..16</a> %e A221258 Some solutions for n=3 %e A221258 ..1..2..1....0..2..0....1..2..0....0..2..1....1..2..0....0..2..1....0..2..0 %e A221258 ..0..2..0....1..2..0....0..2..2....1..2..1....1..2..0....0..2..1....1..2..0 %e A221258 ..0..2..1....2..2..0....0..2..0....0..2..1....0..2..2....1..2..0....1..2..1 %e A221258 ..1..2..0....0..2..1....0..2..1....0..2..0....0..2..0....0..2..1....1..2..0 %K A221258 nonn %O A221258 1,2 %A A221258 _R. H. Hardin_ Jan 06 2013