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%I #8 Sep 24 2018 02:47:33
%S 0,2,8,26,84,272,882,2862,9290,30160,97922,317940,1032328,3351922,
%T 10883582,35338706,114743960,372571146,1209730676,3927970464,
%U 12754039410,41412104942,134464258714,436602703328,1417640069298,4603048385236
%N Number of n X 2 0..3 arrays x(i,j) with each element horizontally, vertically or antidiagonally next to at least one element with value (x(i,j)+1) mod 4, no adjacent elements equal, and upper left element zero.
%H R. H. Hardin, <a href="/A230904/b230904.txt">Table of n, a(n) for n = 1..210</a>
%F Empirical: a(n) = 5*a(n-1) -6*a(n-2) +a(n-3) for n>4.
%F Empirical g.f.: 2*x^2*(1 - x - x^2) / (1 - 5*x + 6*x^2 - x^3). - _Colin Barker_, Sep 22 2018
%e Some solutions for n=4:
%e ..0..1....0..1....0..3....0..1....0..1....0..1....0..1....0..3....0..3....0..1
%e ..2..0....3..2....1..2....2..3....2..0....2..3....2..3....1..0....1..2....3..2
%e ..3..2....0..3....0..3....1..0....3..1....0..1....0..2....2..3....0..1....0..1
%e ..0..1....1..2....2..1....2..3....2..0....3..2....1..0....1..0....3..2....3..2
%Y Column 2 of A230910.
%K nonn
%O 1,2
%A _R. H. Hardin_, Nov 01 2013
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