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 A274797 #7 Apr 19 2020 23:49:00 %S A274797 1,3,30,596,22988,1774372,273764292,85071335388,53278240463204, %T A274797 67444355089828632,172664716787589924632,895256317336401964070392, %U A274797 9404595196718819502562934668,200324135427294084369446897344852 %N A274797 Number of n X n 0..2 arrays with no element equal to any value at offset (-1,-2) (-2,-1) (0,-1) or (-1,0) and new values introduced in order 0..2. %C A274797 Diagonal of A274803. %H A274797 R. H. Hardin, <a href="/A274797/b274797.txt">Table of n, a(n) for n = 1..15</a> %e A274797 Some solutions for n=4 %e A274797 ..0..1..2..1. .0..1..0..1. .0..1..0..1. .0..1..2..1. .0..1..2..0 %e A274797 ..1..0..1..2. .1..2..1..0. .1..0..2..0. .1..0..1..0. .1..2..1..2 %e A274797 ..2..1..0..1. .2..1..2..1. .0..2..0..1. .0..1..0..1. .2..1..2..1 %e A274797 ..1..0..1..0. .1..0..1..0. .1..0..1..0. .1..2..1..0. .1..2..0..2 %Y A274797 Cf. A274803. %K A274797 nonn %O A274797 1,2 %A A274797 _R. H. Hardin_, Jul 07 2016