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 A269647 #6 Aug 12 2016 06:54:17 %S A269647 6,74,574,4564,41526,419516,4351224,45696410,485785550,5235947490, %T A269647 57045797346,626684612988,6931703318082,77128097640376, %U A269647 862658820597866,9692104806070332,109322097799502508,1237402642148758338 %N A269647 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 A269647 Row 3 of A269646. %H A269647 R. H. Hardin, <a href="/A269647/b269647.txt">Table of n, a(n) for n = 1..44</a> %e A269647 Some solutions for n=4 %e A269647 ..2..1..0..0. .0..0..2..2. .2..2..2..0. .0..0..0..2. .0..0..2..1 %e A269647 ..2..2..1..1. .1..1..1..1. .0..0..0..2. .1..1..2..2. .1..2..2..1 %e A269647 ..0..0..2..1. .2..0..0..2. .1..1..1..1. .0..1..1..2. .0..1..2..0 %Y A269647 Cf. A269646. %K A269647 nonn %O A269647 1,1 %A A269647 _R. H. Hardin_, Mar 02 2016