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 A221202 #8 Jun 02 2025 08:11:51 %S A221202 0,49,46,9025,58700,2518569,32085376,848789956,14068757692, %T A221202 311366232004,5733258186854,118412678934081,2273843945394922, %U A221202 45702294155340601,892403786998151272,17744284197389113081,348794591561701410272 %N A221202 Number of 3Xn arrays of occupancy after each element moves to some horizontal, diagonal or antidiagonal neighbor, with no occupancy greater than 2. %C A221202 Row 3 of A221200 %H A221202 R. H. Hardin, <a href="/A221202/b221202.txt">Table of n, a(n) for n = 1..30</a> %e A221202 Some solutions for n=3 %e A221202 ..1..2..1....0..2..1....2..2..0....0..2..0....0..2..0....0..2..1....0..2..1 %e A221202 ..1..2..0....0..2..1....0..2..0....1..2..2....1..2..0....1..2..1....0..2..1 %e A221202 ..0..2..0....1..2..0....0..2..1....0..2..0....1..2..1....0..2..0....0..2..1 %K A221202 nonn %O A221202 1,2 %A A221202 _R. H. Hardin_ Jan 04 2013