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 A266456 #6 Aug 12 2016 06:53:59 %S A266456 1,5,39,357,3471,35003,362265,3821877,40918431,443234475,4847042025, %T A266456 53425329675,592800026625,6615155585925,74183656771239, %U A266456 835491101084757,9445356930180735,107140324945955483,1218962144543118009 %N A266456 Number of 3Xn arrays containing n copies of 0..3-1 with no element 1 greater than its north neighbor modulo 3 and the upper left element equal to 0. %C A266456 Row 3 of A266455. %H A266456 R. H. Hardin, <a href="/A266456/b266456.txt">Table of n, a(n) for n = 1..93</a> %e A266456 Some solutions for n=4 %e A266456 ..0..1..0..1....0..1..1..0....0..0..2..2....0..0..1..0....0..0..1..2 %e A266456 ..2..0..0..1....2..1..1..2....2..0..1..1....2..2..1..2....2..0..1..2 %e A266456 ..2..2..2..1....2..0..0..2....1..2..1..0....2..1..0..1....1..2..0..1 %Y A266456 Cf. A266455. %K A266456 nonn %O A266456 1,2 %A A266456 _R. H. Hardin_, Dec 29 2015