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 A269138 #6 Feb 20 2016 06:50:05 %S A269138 60,1164,18556,275796,3924212,54199284,732561916,9740150372, %T A269138 127846717716,1660741102212,21389485726684,273519303765844, %U A269138 3476418550368820,43954347343683220,553215363420258236,6935081471870462788 %N A269138 Number of nX3 0..3 arrays with some element plus some horizontally, antidiagonally or vertically adjacent neighbor totalling three no more than once. %C A269138 Column 3 of A269143. %H A269138 R. H. Hardin, <a href="/A269138/b269138.txt">Table of n, a(n) for n = 1..210</a> %F A269138 Empirical: a(n) = 26*a(n-1) -199*a(n-2) +408*a(n-3) -463*a(n-4) +322*a(n-5) -141*a(n-6) +36*a(n-7) -4*a(n-8) for n>9 %e A269138 Some solutions for n=3 %e A269138 ..3..2..2. .1..0..0. .0..0..2. .1..1..1. .3..1..0. .1..1..3. .1..3..1 %e A269138 ..3..2..2. .2..0..2. .1..3..3. .0..3..1. .3..0..2. .3..3..3. .1..1..3 %e A269138 ..3..3..2. .0..2..0. .3..1..1. .1..1..3. .2..0..0. .2..2..2. .1..0..1 %Y A269138 Cf. A269143. %K A269138 nonn %O A269138 1,1 %A A269138 _R. H. Hardin_, Feb 20 2016