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 A233067 #8 Jul 23 2025 07:50:48 %S A233067 1,9,582,164495,194998895,975239425635,20656955820980290, %T A233067 1857471420698911806909,710147877110621514637926027, %U A233067 1155599363385647621950232861908393 %N A233067 Number of n X n 0..3 arrays with no element x(i,j) adjacent to value 3-x(i,j) horizontally, antidiagonally or vertically, top left element zero, and 1 appearing before 2 in row major order. %C A233067 Diagonal of A233073 %H A233067 R. H. Hardin, <a href="/A233067/b233067.txt">Table of n, a(n) for n = 1..11</a> %e A233067 Some solutions for n=4 %e A233067 ..0..0..1..0....0..0..0..1....0..0..1..0....0..0..1..3....0..1..0..0 %e A233067 ..0..0..0..2....0..0..0..0....0..1..1..0....1..1..1..1....0..1..1..1 %e A233067 ..0..0..2..3....0..2..2..2....1..1..1..1....3..1..3..3....1..0..1..1 %e A233067 ..0..2..3..1....0..2..3..2....0..1..1..3....3..1..3..1....1..1..1..0 %K A233067 nonn %O A233067 1,2 %A A233067 _R. H. Hardin_, Dec 03 2013