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 A269480 #6 Aug 12 2016 06:54:17 %S A269480 4,54,574,6404,72110,816583,9323584,107089479,1236171969,14324836704, %T A269480 166516037345,1940477033553,22659370920439,265044574417791, %U A269480 3104569328697374,36408281098910933,427405044547342278 %N A269480 Number of 3Xn arrays containing n copies of 0..3-1 avoiding the pattern down-up in every row and equal-up in every column. %C A269480 Row 3 of A269479. %H A269480 R. H. Hardin, <a href="/A269480/b269480.txt">Table of n, a(n) for n = 1..49</a> %e A269480 Some solutions for n=4 %e A269480 ..2..0..1..0. .1..1..0..0. .2..0..1..2. .2..0..1..1. .1..0..2..0 %e A269480 ..2..1..1..0. .2..1..0..0. .2..0..1..2. .2..0..2..2. .1..2..1..0 %e A269480 ..0..2..2..1. .1..2..2..2. .1..1..0..0. .0..1..0..1. .0..2..1..2 %Y A269480 Cf. A269479. %K A269480 nonn %O A269480 1,1 %A A269480 _R. H. Hardin_, Feb 27 2016