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 A269180 #8 Jan 19 2019 12:07:59 %S A269180 4,48,384,2736,18336,118032,739008,4533744,27384288,163381968, %T A269180 965118720,5654345136,32898781728,190290667152,1095084877632, %U A269180 6274151751024,35807326610016,203653219107408,1154714957732736,6529188836867376 %N A269180 Number of n X 2 0..3 arrays with some element plus some horizontally, diagonally, antidiagonally or vertically adjacent neighbor totalling three exactly once. %H A269180 R. H. Hardin, <a href="/A269180/b269180.txt">Table of n, a(n) for n = 1..210</a> %F A269180 Empirical: a(n) = 10*a(n-1) - 21*a(n-2) - 20*a(n-3) - 4*a(n-4) for n>5. %F A269180 Empirical g.f.: 4*x*(1 - x)^2*(1 + 2*x)^2 / (1 - 5*x - 2*x^2)^2. - _Colin Barker_, Jan 19 2019 %e A269180 Some solutions for n=4: %e A269180 ..1..1. .2..3. .3..3. .1..0. .3..0. .0..2. .1..1. .2..0. .1..0. .1..1 %e A269180 ..0..0. .2..0. .1..3. .2..0. .2..2. .2..0. .1..3. .1..0. .0..0. .0..0 %e A269180 ..2..0. .2..0. .0..1. .0..0. .2..0. .1..0. .1..3. .0..0. .1..0. .1..0 %e A269180 ..3..2. .2..2. .0..1. .0..0. .2..0. .0..0. .1..0. .0..0. .3..1. .1..3 %Y A269180 Column 2 of A269186. %K A269180 nonn %O A269180 1,1 %A A269180 _R. H. Hardin_, Feb 20 2016