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 A268974 #4 Feb 16 2016 13:49:26 %S A268974 81,1728,15552,136080,1125360,9093528,72081792,563173128,4349328912, %T A268974 33272350344,252534743280,1904015932416,14274182767248, %U A268974 106487231224248,791006745522096,5853579437553624,43172409083833728,317460508504648992 %N A268974 Number of 4Xn 0..2 arrays with some element plus some horizontally or antidiagonally adjacent neighbor totalling two not more than once. %C A268974 Row 4 of A268971. %H A268974 R. H. Hardin, <a href="/A268974/b268974.txt">Table of n, a(n) for n = 1..210</a> %F A268974 Empirical: a(n) = 18*a(n-1) -111*a(n-2) +282*a(n-3) -333*a(n-4) +180*a(n-5) -36*a(n-6) for n>12 %e A268974 Some solutions for n=4 %e A268974 ..2..1..0..0. .0..0..1..2. .0..1..0..0. .2..1..0..0. .0..1..2..1 %e A268974 ..0..0..1..2. .0..2..1..2. .0..0..0..0. .0..0..0..0. .2..1..0..0 %e A268974 ..1..2..2..2. .1..0..1..0. .2..1..0..0. .1..0..1..1. .0..0..1..2 %e A268974 ..2..1..0..0. .0..0..0..0. .2..1..0..1. .1..0..0..0. .1..0..0..0 %Y A268974 Cf. A268971. %K A268974 nonn %O A268974 1,1 %A A268974 _R. H. Hardin_, Feb 16 2016