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A230813 Number of n X 2 0..2 arrays x(i,j) with each element horizontally or vertically next to at least one element with value (x(i,j)+1) mod 3 and at least one element with value (x(i,j)-1) mod 3, and upper left element zero. 2
0, 0, 2, 0, 2, 12, 18, 56, 170, 420, 1162, 3200, 8562, 23292, 63298, 171336, 464890, 1261140, 3419322, 9274000, 25152322, 68211372, 184993778, 501712216, 1360654410, 3690150660, 10007829482, 27141578400, 73608971282, 199630236252 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

Column 2 of A230819.

LINKS

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

FORMULA

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

Empirical g.f.: 2*x^3*(1 - 2*x) / (1 - 2*x - x^2 - 4*x^3 + 4*x^4). - Colin Barker, Mar 17 2018

EXAMPLE

All solutions for n=5:

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

..2..2....1..1

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

..2..2....1..1

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

CROSSREFS

Cf. A230819.

Sequence in context: A250406 A107094 A122496 * A177113 A281205 A285152

Adjacent sequences:  A230810 A230811 A230812 * A230814 A230815 A230816

KEYWORD

nonn

AUTHOR

R. H. Hardin, Oct 30 2013

STATUS

approved

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Last modified October 22 19:53 EDT 2019. Contains 328319 sequences. (Running on oeis4.)