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%I #8 Oct 06 2018 05:30:24
%S 9,18,54,144,396,1080,2952,8064,22032,60192,164448,449280,1227456,
%T 3353472,9161856,25030656,68385024,186831360,510432768,1394528256,
%U 3809922048,10408900608,28437645312,77693091840,212261474304
%N Number of 2 X n 0..2 arrays with no element x(i,j) adjacent to value 2-x(i,j) horizontally, diagonally or antidiagonally.
%H R. H. Hardin, <a href="/A232921/b232921.txt">Table of n, a(n) for n = 1..210</a>
%F Empirical: a(n) = 2*a(n-1) + 2*a(n-2).
%F Conjectures from _Colin Barker_, Oct 06 2018: (Start)
%F G.f.: 9*x / (1 - 2*x - 2*x^2).
%F a(n) = (-3)*(sqrt(3)*((1-sqrt(3))^n - (1+sqrt(3))^n)) / 2.
%F (End)
%e Some solutions for n=5:
%e ..0..1..2..2..2....2..1..2..2..1....2..1..0..0..1....2..2..1..0..1
%e ..2..1..2..1..2....0..1..2..2..1....2..1..0..0..0....2..2..1..0..1
%Y Row 2 of A232920.
%K nonn
%O 1,1
%A _R. H. Hardin_, Dec 02 2013
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