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 A268143 #8 Apr 28 2021 12:52:49 %S A268143 0,0,0,8,32,238,1488,9778,91628,685364,5183732,43292440,341958992, %T A268143 2698310688,22015262376,177423576662,1428012268840,11630157575168, %U A268143 94604167006872,769682941957332,6291338814803772,51481101154395306 %N A268143 Number of 3 X n arrays containing n copies of 0..3-1 with every element equal to at least one diagonal or antidiagonal neighbor and the top left element equal to 0. %C A268143 Row 3 of A268142. %H A268143 R. H. Hardin, <a href="/A268143/b268143.txt">Table of n, a(n) for n = 1..52</a> %e A268143 Some solutions for n=4 %e A268143 ..0..1..0..2....0..1..2..1....0..2..1..2....0..1..1..2....0..2..0..1 %e A268143 ..1..0..2..1....2..0..1..2....1..0..2..1....1..0..2..1....2..0..1..2 %e A268143 ..0..2..1..2....0..2..0..1....0..1..0..2....0..2..0..2....0..1..2..1 %Y A268143 Cf. A268142. %K A268143 nonn %O A268143 1,4 %A A268143 _R. H. Hardin_, Jan 27 2016