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 A206688 #7 Jul 22 2025 19:36:25 %S A206688 2,36,176,916,4704,24492,127008,660888,3436488,17884080,93059016, %T A206688 484334480,2520695968,13119605656,68284077520,355405952496, %U A206688 1849822022856,9628019156288,50112266984832,260826450827576,1357560738338768 %N A206688 Number of nX4 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 A206688 Column 4 of A206692 %H A206688 R. H. Hardin, <a href="/A206688/b206688.txt">Table of n, a(n) for n = 1..210</a> %F A206688 Empirical: a(n) = 8*a(n-1) -8*a(n-2) -48*a(n-3) +48*a(n-4) +140*a(n-5) +67*a(n-6) -968*a(n-7) +1564*a(n-8) -586*a(n-9) -1008*a(n-10) -32*a(n-11) +1304*a(n-12) +80*a(n-13) -512*a(n-14) for n>15 %e A206688 Some solutions for n=4 %e A206688 ..0..1..2..3....0..1..2..3....0..1..2..3....0..1..2..3....0..1..2..3 %e A206688 ..2..3..0..2....3..0..1..2....1..0..3..1....2..3..1..0....2..3..0..1 %e A206688 ..3..2..1..0....1..2..3..1....2..3..1..0....3..2..0..1....1..0..3..2 %e A206688 ..0..1..2..3....0..1..2..0....3..1..0..2....0..1..2..3....0..1..2..3 %K A206688 nonn %O A206688 1,1 %A A206688 _R. H. Hardin_ Feb 11 2012