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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
0, 6, 28, 168, 960, 5530, 31808, 183000, 1052800, 6056806, 34845028, 200464768, 1153281360, 6634871130, 38170663608, 219597266000, 1263351345600, 7268107893606, 41813698570028, 240555783389368, 1383926485841760 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

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

FORMULA

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

Empirical g.f.: 2*x^2*(3 - 4*x) / ((1 + x)*(1 - 7*x + 7*x^2 + x^3)). - Colin Barker, Feb 07 2019

EXAMPLE

Some solutions for n=4:

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

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

CROSSREFS

Row 2 of A278014.

Sequence in context: A045722 A047129 A173081 * A169723 A052395 A034660

Adjacent sequences:  A278012 A278013 A278014 * A278016 A278017 A278018

KEYWORD

nonn

AUTHOR

R. H. Hardin, Nov 08 2016

STATUS

approved

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Last modified November 20 23:06 EST 2019. Contains 329348 sequences. (Running on oeis4.)