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A221276 Number of 2 X n arrays of occupancy after each element moves to some horizontal, diagonal or antidiagonal neighbor, with every occupancy equal to zero or two. 1
0, 4, 4, 25, 52, 196, 520, 1681, 4840, 14884, 44044, 133225, 397852, 1196836, 3585040, 10764961, 32278480, 96864964, 290545684, 871725625, 2615029252, 7845353476, 23535617560, 70607649841, 211821620920, 635467254244, 1906397776924 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Row 2 of A221275.

LINKS

R. H. Hardin, Table of n, a(n) for n = 1..94

FORMULA

Empirical: a(n) = 4*a(n-1) - 12*a(n-3) + 9*a(n-4).

Empirical g.f.: x^2*(2 - 3*x)^2 / ((1 - x)*(1 - 3*x)*(1 - 3*x^2)). - Colin Barker, Aug 04 2018

EXAMPLE

Some solutions for n=4:

..0..0..0..2....0..2..2..0....2..2..2..0....2..0..0..0....0..2..2..0

..2..2..2..0....2..0..0..2....0..0..0..2....0..2..2..2....0..2..2..0

CROSSREFS

Cf. A221275.

Sequence in context: A269097 A307552 A171633 * A117429 A132650 A112953

Adjacent sequences:  A221273 A221274 A221275 * A221277 A221278 A221279

KEYWORD

nonn

AUTHOR

R. H. Hardin, Jan 09 2013

STATUS

approved

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Last modified November 30 02:42 EST 2020. Contains 338781 sequences. (Running on oeis4.)