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%I #8 Oct 06 2018 11:37:57
%S 4,21,129,771,4629,27771,166629,999771,5998629,35991771,215950629,
%T 1295703771,7774222629,46645335771,279872014629,1679232087771,
%U 10075392526629,60452355159771,362714130958629,2176284785751771
%N Number of 2 X n 0..3 arrays with no element x(i,j) adjacent to value 3-x(i,j) horizontally, diagonally or antidiagonally, and top left element zero.
%H R. H. Hardin, <a href="/A232956/b232956.txt">Table of n, a(n) for n = 1..210</a>
%F Empirical: a(n) = 5*a(n-1) + 6*a(n-2).
%F Conjectures from _Colin Barker_, Oct 06 2018: (Start)
%F G.f.: x*(4 + x) / ((1 + x)*(1 - 6*x)).
%F a(n) = (25*6^n - 18) / 42 for n even.
%F a(n) = (25*6^n + 18) / 42 for n odd.
%F (End)
%e Some solutions for n=5:
%e ..0..1..0..2..3....0..0..0..0..1....0..0..0..1..0....0..1..1..1..0
%e ..3..2..0..2..2....0..1..1..0..2....0..0..1..1..0....0..0..0..1..0
%Y Row 2 of A232955.
%K nonn
%O 1,1
%A _R. H. Hardin_, Dec 02 2013
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