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 A274744 #6 Apr 21 2020 12:40:02 %S A274744 1,3,34,813,40242,4190533,920432562,427529873959,420708712370442, %T A274744 878018029249193808,3889681900917706414509,36599212212994279601355491, %U A274744 731787586726658710118188021426 %N A274744 Number of n X n 0..2 arrays with no element equal to any value at offset (-1,-2), (0,-1) or (-1,0) and new values introduced in order 0..2. %C A274744 Diagonal of A274749. %e A274744 Some solutions for n=4 %e A274744 ..0..1..2..0. .0..1..0..1. .0..1..0..2. .0..1..0..2. .0..1..0..1 %e A274744 ..1..2..1..2. .1..0..1..0. .2..0..2..0. .1..0..1..0. .2..0..1..0 %e A274744 ..0..1..0..1. .0..1..0..2. .1..2..1..2. .0..1..0..1. .0..1..0..1 %e A274744 ..2..0..1..2. .1..0..1..0. .2..0..2..1. .2..0..1..0. .1..2..1..0 %Y A274744 Cf. A274749. %K A274744 nonn %O A274744 1,2 %A A274744 _R. H. Hardin_, Jul 04 2016