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 A269103 #9 Mar 21 2018 12:17:26 %S A269103 16,180,1740,15540,132300,1090740,8787660,69580980,543538380, %T A269103 4200069300,32167589580,244542858420,1847388128460,13880833735860, %U A269103 103809654007500,773174303047860,5737767196302540,42443199898890420,313054205965641420 %N A269103 Number of n X 2 0..3 arrays with some element plus some horizontally or vertically adjacent neighbor totalling three no more than once. %C A269103 Column 2 of A269109. %H A269103 R. H. Hardin, <a href="/A269103/b269103.txt">Table of n, a(n) for n = 1..210</a> %F A269103 Empirical: a(n) = 14*a(n-1) - 49*a(n-2) for n>3. %F A269103 Conjectures from _Colin Barker_, Mar 21 2018: (Start) %F A269103 G.f.: 4*x*(4 - 11*x + x^2) / (1 - 7*x)^2. %F A269103 a(n) = 60*7^(n-3)*(8*n+5) for n>1. %F A269103 (End) %e A269103 Some solutions for n=4: %e A269103 ..2..2. .2..0. .2..2. .1..0. .3..3. .3..1. .1..3. .3..1. .1..3. .1..0 %e A269103 ..0..2. .2..0. .2..3. .3..1. .3..1. .3..3. .3..1. .3..1. .1..3. .3..1 %e A269103 ..1..0. .0..2. .2..3. .1..1. .2..2. .2..2. .3..3. .1..3. .0..1. .0..1 %e A269103 ..1..0. .1..0. .1..1. .1..1. .3..3. .3..0. .1..3. .3..1. .0..0. .2..0 %Y A269103 Cf. A269109. %K A269103 nonn %O A269103 1,1 %A A269103 _R. H. Hardin_, Feb 19 2016