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 A209093 #9 Jun 09 2023 21:35:36 %S A209093 1,11,1326,849548,2896732704,52675800891748,5112092569118325704, %T A209093 2648032740541890194825808,7321189749687647765176559002512, %U A209093 108035622217854017447945402727365754008 %N A209093 Number of n X n 0..2 arrays with new values 0..2 introduced in row major order and no element equal to more than one of its immediate leftward or upward or right-upward antidiagonal neighbors. %C A209093 Diagonal of A209100. %H A209093 R. H. Hardin, <a href="/A209093/b209093.txt">Table of n, a(n) for n = 1..13</a> %e A209093 Some solutions for n=4 %e A209093 ..0..1..0..2....0..0..0..0....0..0..0..1....0..0..0..0....0..0..0..1 %e A209093 ..1..2..0..1....1..1..1..0....2..1..2..0....1..1..1..0....1..1..2..0 %e A209093 ..1..0..1..2....2..2..1..2....0..2..1..1....0..2..0..2....0..1..2..2 %e A209093 ..0..1..2..0....0..0..2..0....2..0..0..1....2..0..1..1....0..0..0..2 %Y A209093 Cf. A209100. %K A209093 nonn %O A209093 1,2 %A A209093 _R. H. Hardin_, Mar 05 2012