A221276 - OEIS

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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.

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: