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 A230735 #6 Jul 23 2025 05:59:01 %S A230735 2,66,2106,320970,43853402,36695929036,26681634560690, %T A230735 121531720205091748,479398570293769095556,11869733818244916838154264 %N A230735 Number of (n+3)X(n+3) 0..2 black square subarrays x(i,j) with each element diagonally or antidiagonally next to at least one element with value (x(i,j)+1) mod 3, and upper left element zero. %C A230735 Diagonal of A230739 %e A230735 Some solutions for n=3 %e A230735 ..x..0..x..0..x..1....x..0..x..1..x..0....x..0..x..2..x..2....x..0..x..2..x..2 %e A230735 ..2..x..1..x..2..x....1..x..2..x..1..x....2..x..1..x..0..x....2..x..1..x..0..x %e A230735 ..x..2..x..1..x..1....x..2..x..1..x..2....x..2..x..0..x..1....x..1..x..0..x..1 %e A230735 ..0..x..1..x..2..x....1..x..0..x..0..x....0..x..2..x..2..x....2..x..2..x..2..x %e A230735 ..x..1..x..0..x..1....x..0..x..1..x..2....x..1..x..2..x..1....x..0..x..2..x..1 %e A230735 ..0..x..2..x..0..x....2..x..2..x..0..x....0..x..1..x..0..x....2..x..1..x..0..x %K A230735 nonn %O A230735 1,1 %A A230735 _R. H. Hardin_, Oct 28 2013