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 A275221 #6 Apr 21 2020 12:44:26 %S A275221 1,6,61,1302,64248,6534900,1368326231,608741311725,563051463762052 %N A275221 Number of n X n 0..2 arrays with no element equal to any value at offset (-2,-1), (-2,1) or (-1,0) and new values introduced in order 0..2. %C A275221 Diagonal of A275228. %e A275221 Some solutions for n=4 %e A275221 ..0..1..2..1. .0..0..1..2. .0..1..0..2. .0..1..0..2. .0..1..0..2 %e A275221 ..1..0..1..2. .2..1..2..1. .1..0..1..1. .1..0..2..0. .1..2..1..0 %e A275221 ..0..1..0..1. .1..2..1..0. .2..1..0..2. .0..2..0..1. .2..1..0..1 %e A275221 ..1..0..1..2. .2..0..2..1. .1..2..2..0. .2..0..1..0. .1..0..1..0 %Y A275221 Cf. A275228. %K A275221 nonn %O A275221 1,2 %A A275221 _R. H. Hardin_, Jul 20 2016