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 A269091 #7 Mar 21 2018 11:53:10 %S A269091 4,96,1152,11424,103488,889056,7375872,59698464,474360768,3715826016, %T A269091 28777886592,220814937504,1681292682048,12718165610976,95670977133312, %U A269091 716203564928544,5338972029467328,39651633731043936,293513242790716032 %N A269091 Number of n X 2 0..3 arrays with some element plus some horizontally or vertically adjacent neighbor totalling three exactly once. %C A269091 Column 2 of A269097. %H A269091 R. H. Hardin, <a href="/A269091/b269091.txt">Table of n, a(n) for n = 1..210</a> %F A269091 Empirical: a(n) = 14*a(n-1) -49*a(n-2) for n>3. %F A269091 Conjectures from _Colin Barker_, Mar 21 2018: (Start) %F A269091 G.f.: 4*x*(1 + 10*x + x^2) / (1 - 7*x)^2. %F A269091 a(n) = 96*7^(n-3)*(5*n-3) for n>1. %F A269091 (End) %e A269091 Some solutions for n=4: %e A269091 ..2..0. .2..2. .3..3. .3..3. .1..3. .3..3. .2..2. .3..2. .3..3. .1..3 %e A269091 ..1..1. .2..2. .2..3. .2..2. .3..1. .0..1. .3..2. .2..3. .3..3. .0..1 %e A269091 ..1..1. .1..0. .3..1. .1..3. .2..2. .1..0. .1..0. .0..1. .1..0. .0..2 %e A269091 ..3..3. .3..2. .2..2. .3..3. .3..3. .0..1. .1..2. .0..2. .3..2. .2..2 %Y A269091 Cf. A269097. %K A269091 nonn %O A269091 1,1 %A A269091 _R. H. Hardin_, Feb 19 2016