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 A207980 #7 Mar 15 2023 16:27:06 %S A207980 15,1080,587208,953124784,3410310590912,22727131144960768, %T A207980 253335104721267417984,4382417290595586402531584, %U A207980 111319355727036703898865465344,3978834602846298450265688566196224,193442461762324413798952526604793292800 %N A207980 Number of n X 4 nonnegative integer arrays with new values 0 upwards introduced in row major order and no element equal to any diagonal or antidiagonal neighbor (colorings ignoring permutations of colors). %H A207980 Andrew Howroyd, <a href="/A207980/b207980.txt">Table of n, a(n) for n = 1..140</a> %e A207980 Some solutions for n=4 %e A207980 ..0..0..0..0....0..1..0..0....0..0..0..0....0..0..1..0....0..0..0..0 %e A207980 ..1..1..2..1....2..1..2..1....1..1..2..1....1..2..1..0....1..1..1..1 %e A207980 ..0..3..0..0....0..0..0..0....2..0..0..0....0..0..1..0....2..0..0..0 %e A207980 ..4..1..1..1....1..1..1..1....1..1..1..2....2..2..1..0....1..1..1..1 %Y A207980 Column 4 of A207981. %K A207980 nonn %O A207980 1,1 %A A207980 _R. H. Hardin_, Feb 22 2012 %E A207980 Terms a(8) and beyond from _Andrew Howroyd_, Mar 15 2023