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 A221259 #6 Jun 02 2025 08:13:50 %S A221259 0,256,418,1612900,78633756,22466712321,2294073688498,399487764096100, %T A221259 51031822108216122,7730096571419434884,1061888266253693915768, %U A221259 154122481474602369093121,21681358901642544133423968 %N A221259 Number of 5Xn arrays of occupancy after each element moves to some horizontal or antidiagonal neighbor, with no occupancy greater than 2. %C A221259 Row 5 of A221255 %H A221259 R. H. Hardin, <a href="/A221259/b221259.txt">Table of n, a(n) for n = 1..15</a> %e A221259 Some solutions for n=3 %e A221259 ..1..2..0....0..2..1....0..2..0....0..2..1....1..2..0....0..2..1....0..2..2 %e A221259 ..0..2..2....0..2..1....1..2..0....1..2..1....1..2..1....0..2..0....0..2..1 %e A221259 ..0..2..1....1..2..0....1..2..2....0..2..0....0..2..0....1..2..1....0..2..0 %e A221259 ..0..2..0....0..2..0....0..2..0....0..2..1....0..2..1....1..2..1....0..2..2 %e A221259 ..1..2..0....2..2..0....0..2..1....0..2..1....1..2..0....0..2..0....0..2..0 %K A221259 nonn %O A221259 1,2 %A A221259 _R. H. Hardin_ Jan 06 2013