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 A221696 #6 Jul 23 2025 02:07:38 %S A221696 1,987,63676,7033429,659020617,64509677154,6233675847228, %T A221696 604346923784252,58538232535028520,5671250113728678882, %U A221696 549411330594167686392,53225495837252796349285,5156336905625087231654148 %N A221696 Number of 4Xn arrays of occupancy after each element stays put or moves to some horizontal or antidiagonal neighbor, without consecutive moves in the same direction. %C A221696 Row 4 of A221693 %H A221696 R. H. Hardin, <a href="/A221696/b221696.txt">Table of n, a(n) for n = 1..18</a> %e A221696 Some solutions for n=3 %e A221696 ..2..0..0....2..0..1....0..1..1....1..0..0....0..4..1....1..0..0....0..3..2 %e A221696 ..0..3..1....1..1..0....2..3..0....1..4..0....0..0..1....2..2..1....0..0..1 %e A221696 ..1..0..1....2..0..0....0..0..0....2..0..2....2..1..0....0..2..0....1..2..1 %e A221696 ..1..3..0....1..3..1....2..1..2....0..1..1....0..3..0....1..3..0....1..0..1 %K A221696 nonn %O A221696 1,2 %A A221696 _R. H. Hardin_ Jan 22 2013