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 A265452 #4 Dec 09 2015 09:57:41 %S A265452 2,18,250,3358,42282,502154,5710302,62782966,672520310,7056533978, %T A265452 72819524370,741279145398,7460955607878,74381377429158, %U A265452 735539563061590,7222916531541006,70499118369836786,684459097597365542 %N A265452 Number of nX2 0..n+2-2 arrays with each element differing from its horizontal and vertical neighbors by one or two. %C A265452 Column 2 of A265458. %H A265452 R. H. Hardin, <a href="/A265452/b265452.txt">Table of n, a(n) for n = 1..210</a> %e A265452 Some solutions for n=4 %e A265452 ..1..2....3..1....1..0....4..3....3..2....2..3....2..0....1..3....4..2....3..2 %e A265452 ..2..3....4..2....0..2....2..1....2..1....3..4....0..1....2..4....3..1....1..0 %e A265452 ..1..2....2..1....2..3....1..3....1..2....4..2....1..2....1..2....1..3....0..1 %e A265452 ..3..4....1..3....3..1....0..1....3..4....2..1....2..3....2..1....3..1....2..3 %Y A265452 Cf. A265458. %K A265452 nonn %O A265452 1,1 %A A265452 _R. H. Hardin_, Dec 09 2015