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 A208306 #7 May 18 2020 19:25:39 %S A208306 1,203,678570,46538017584,17131843186425504,21183598567292002167082, %T A208306 67939294184937980415465539016,479196921365748673300774676923278618, %U A208306 6626004995909411145707148239379062019989108,164986885310084515129040822858386474548745376110410 %N A208306 Number of 6 X n nonnegative integer arrays with new values 0 upwards introduced in row major order and no element equal to any horizontal or antidiagonal neighbor (colorings ignoring permutations of colors). %H A208306 Andrew Howroyd, <a href="/A208306/b208306.txt">Table of n, a(n) for n = 0..50</a> %e A208306 Some solutions for n=4: %e A208306 ..0..1..2..0....0..1..0..1....0..1..0..1....0..1..0..1....0..1..0..1 %e A208306 ..0..1..2..0....0..1..0..1....2..1..0..1....0..1..0..1....2..1..0..1 %e A208306 ..0..1..2..0....0..1..0..1....0..1..0..1....2..1..0..1....0..3..0..3 %e A208306 ..0..1..2..0....2..1..3..0....2..1..2..0....0..1..2..0....0..1..0..1 %e A208306 ..0..1..2..0....0..1..2..0....0..1..2..0....0..1..2..0....3..1..0..1 %e A208306 ..0..1..2..3....0..1..2..0....0..3..1..0....0..1..2..0....0..1..0..1 %Y A208306 Row 6 of A208301. %K A208306 nonn %O A208306 0,2 %A A208306 _R. H. Hardin_, Feb 25 2012 %E A208306 a(0)=1 prepended and terms a(6) and beyond from _Andrew Howroyd_, May 18 2020