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 A208099 #10 May 18 2020 18:58:50 %S A208099 1,15,500,192328,235862938,677352910013,3773408294000427, %T A208099 36179066767453804155,549736601190850705047301, %U A208099 12463226118187748082979153202,402612019211536786633308878052340,17870804510325656079748707416649732732,1058340866272922899343613575761029687845720 %N A208099 Number of 4 X n nonnegative integer arrays with new values 0 upwards introduced in row major order and no element equal to any horizontal, diagonal or antidiagonal neighbor (colorings ignoring permutations of colors). %H A208099 Andrew Howroyd, <a href="/A208099/b208099.txt">Table of n, a(n) for n = 0..100</a> %e A208099 Some solutions for n=4: %e A208099 ..0..1..0..1....0..1..0..1....0..1..0..1....0..1..0..1....0..1..0..1 %e A208099 ..0..1..0..1....0..1..0..2....0..1..0..1....2..1..0..1....2..1..0..1 %e A208099 ..0..1..2..1....2..1..0..1....2..1..0..2....0..3..0..1....0..1..2..1 %e A208099 ..0..1..3..1....0..1..0..2....0..1..0..1....4..1..0..1....0..1..0..1 %Y A208099 Row 4 of A208096. %K A208099 nonn %O A208099 0,2 %A A208099 _R. H. Hardin_, Feb 23 2012 %E A208099 a(0)=1 prepended and terms a(6) and beyond from _Andrew Howroyd_, May 18 2020