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 A278015 Number of 2 X n 0..2 arrays with every element plus 1 mod 3 equal to some element at offset (-1,-1) (-1,0) (-1,1) (0,-1) (0,1) or (1,0), with upper left element zero. 1

%I

%S 0,6,28,168,960,5530,31808,183000,1052800,6056806,34845028,200464768,

%T 1153281360,6634871130,38170663608,219597266000,1263351345600,

%U 7268107893606,41813698570028,240555783389368,1383926485841760

%N Number of 2 X n 0..2 arrays with every element plus 1 mod 3 equal to some element at offset (-1,-1) (-1,0) (-1,1) (0,-1) (0,1) or (1,0), with upper left element zero.

%H R. H. Hardin, <a href="/A278015/b278015.txt">Table of n, a(n) for n = 1..210</a>

%F Empirical: a(n) = 6*a(n-1) - 8*a(n-3) - a(n-4).

%F Empirical g.f.: 2*x^2*(3 - 4*x) / ((1 + x)*(1 - 7*x + 7*x^2 + x^3)). - _Colin Barker_, Feb 07 2019

%e Some solutions for n=4:

%e ..0..2..0..1. .0..1..0..2. .0..1..2..0. .0..1..0..2. .0..2..1..0

%e ..1..1..0..2. .1..2..1..1. .2..2..2..1. .1..2..1..0. .1..1..2..1

%Y Row 2 of A278014.

%K nonn

%O 1,2

%A _R. H. Hardin_, Nov 08 2016

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Last modified May 22 06:54 EDT 2022. Contains 353933 sequences. (Running on oeis4.)