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 A208173 #7 Jul 22 2025 21:13:44 %S A208173 187,506493,1496307201,4422202024212,13069424064243420, %T A208173 38625516979536823947,114154269785454920027391, %U A208173 337372761040287875038964700,997075099388051313174129747636 %N A208173 Number of nX6 0..3 arrays with new values 0..3 introduced in row major order and no element equal to more than one of its immediate leftward or upward neighbors. %C A208173 Column 6 of A208175 %H A208173 R. H. Hardin, <a href="/A208173/b208173.txt">Table of n, a(n) for n = 1..210</a> %e A208173 Some solutions for n=4 %e A208173 ..0..0..1..0..0..0....0..1..0..0..1..0....0..0..0..1..0..2....0..0..0..0..1..1 %e A208173 ..0..1..2..1..1..3....1..0..2..3..1..3....2..0..1..3..2..0....2..0..2..2..1..0 %e A208173 ..3..3..2..0..0..2....2..2..1..1..3..2....0..1..0..1..0..1....3..2..3..0..2..3 %e A208173 ..1..1..3..1..0..0....0..1..0..3..0..1....3..3..3..2..3..0....3..0..1..2..3..2 %K A208173 nonn %O A208173 1,1 %A A208173 _R. H. Hardin_ Feb 24 2012