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 A206690 #7 Jul 22 2025 19:36:40 %S A206690 8,376,2816,24492,213788,1915580,17277556,156946368,1429962032, %T A206690 13057140562,119353104128,1091748256156,9990044761998,91434371494388, %U A206690 836958605238016,7661779056726008,70141114109343664,642134221496445414 %N A206690 Number of nX6 0..3 arrays with no element equal to another within two positions in the same row or column, and new values 0..3 introduced in row major order. %C A206690 Column 6 of A206692 %H A206690 R. H. Hardin, <a href="/A206690/b206690.txt">Table of n, a(n) for n = 1..210</a> %e A206690 Some solutions for n=4 %e A206690 ..0..1..2..3..1..0....0..1..2..3..1..2....0..1..2..0..1..3....0..1..2..3..1..0 %e A206690 ..2..3..1..0..2..1....1..0..3..1..0..3....1..0..3..1..2..0....2..3..1..2..3..1 %e A206690 ..1..2..3..1..0..3....2..3..0..2..3..1....3..2..1..3..0..1....1..2..0..1..2..3 %e A206690 ..0..1..2..3..1..0....3..1..2..3..1..2....0..1..2..0..1..2....3..0..2..3..1..2 %K A206690 nonn %O A206690 1,1 %A A206690 _R. H. Hardin_ Feb 11 2012