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A277939

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

0, 3, 14, 74, 377, 1932, 9888, 50619, 259118, 1326434, 6790049, 34758444, 177929400, 910825347, 4662539246, 23867662778, 122179202441, 625438596492, 3201636859344, 16389264488331, 83897082108014, 429471401309714

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OFFSET

1,2

LINKS

R. H. Hardin, Table of n, a(n) for n = 1..210

FORMULA

Empirical: a(n) = 4*a(n-1) + 6*a(n-2) - a(n-3) - 2*a(n-4).

Empirical g.f.: x^2*(3 + 2*x) / ((1 + x)*(1 - 5*x - x^2 + 2*x^3)). - Colin Barker, Feb 06 2019

EXAMPLE

Some solutions for n=4:

..0..1. .0..2. .0..1. .0..2. .0..2. .0..2. .0..1. .0..2. .0..2. .0..2

..2..2. .1..1. .1..2. .1..2. .1..0. .1..1. .0..2. .1..0. .1..1. .1..0