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%I #8 Jan 17 2019 09:20:34
%S 9,60,336,1728,8448,39936,184320,835584,3735552,16515072,72351744,
%T 314572800,1358954496,5838471168,24964497408,106300440576,
%U 450971566080,1906965479424,8040178778112,33809982554112,141836999983104
%N Number of n X 2 0..2 arrays with some element plus some horizontally or antidiagonally adjacent neighbor totalling two not more than once.
%H R. H. Hardin, <a href="/A268965/b268965.txt">Table of n, a(n) for n = 1..210</a>
%F Empirical: a(n) = 8*a(n-1) - 16*a(n-2).
%F Conjectures from _Colin Barker_, Jan 17 2019: (Start)
%F G.f.: 3*x*(3 - 4*x) / (1 - 4*x)^2.
%F a(n) = 4^(n-1) * (6*n+3).
%F (End)
%e Some solutions for n=4:
%e ..0..0. .0..0. .0..1. .2..2. .1..2. .1..0. .2..2. .0..2. .2..1. .0..1
%e ..0..2. .1..1. .0..0. .1..1. .2..0. .0..0. .2..1. .2..1. .0..2. .2..2
%e ..2..2. .2..1. .2..2. .2..2. .0..1. .2..2. .2..1. .0..0. .1..2. .2..0
%e ..1..0. .2..1. .2..2. .2..1. .2..1. .1..0. .2..2. .0..0. .2..2. .1..2
%Y Column 2 of A268971.
%K nonn
%O 1,1
%A _R. H. Hardin_, Feb 16 2016
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