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 A269507 #6 Aug 12 2016 06:54:17 %S A269507 4,54,420,3088,25226,239994,2338286,23240168,232006814,2352889414, %T A269507 24069853302,248560741574,2582277394354,26997628173380, %U A269507 283652378887212,2994183763030920,31727834772912212,337396544704648686 %N A269507 Number of 3Xn arrays containing n copies of 0..3-1 avoiding the pattern down-up in every row and column. %C A269507 Row 3 of A269505. %H A269507 R. H. Hardin, <a href="/A269507/b269507.txt">Table of n, a(n) for n = 1..48</a> %e A269507 Some solutions for n=4 %e A269507 ..1..1..2..0. .1..0..0..1. .0..0..2..1. .0..0..2..2. .0..1..2..1 %e A269507 ..1..1..2..2. .2..1..1..2. .0..2..2..1. .1..2..1..1. .0..2..2..1 %e A269507 ..0..0..0..2. .0..2..2..0. .2..1..1..0. .1..2..0..0. .2..0..0..1 %Y A269507 Cf. A269505. %K A269507 nonn %O A269507 1,1 %A A269507 _R. H. Hardin_, Feb 28 2016