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A269270 Number of n X 2 0..3 arrays with some element plus some horizontally or antidiagonally adjacent neighbor totalling three exactly once. 1
4, 108, 1620, 20412, 236196, 2598156, 27634932, 286978140, 2927177028, 29443957164, 292889889684, 2887057484028, 28242953648100, 274521509459532, 2653707924775476, 25530500379736476, 244598664928443012 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

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

FORMULA

Empirical: a(n) = 18*a(n-1) - 81*a(n-2).

Conjectures from Colin Barker, Jan 20 2019: (Start)

G.f.: 4*x*(1 + 9*x) / (1 - 9*x)^2.

a(n) = 9^(n-1) * (8*n-4).

(End)

EXAMPLE

Some solutions for n=4:

2 3 2 2 3 3 2 2 3 0 2 2 0 0 1 1 1 3 3 1

2 0 2 2 3 1 0 0 0 0 3 1 2 1 0 2 1 1 1 1

3 1 0 0 0 0 1 2 1 0 0 3 0 1 0 2 2 0 3 0

1 0 3 3 3 2 0 0 1 3 1 0 0 0 1 0 1 1 2 2

CROSSREFS

Column 2 of A269276.

Sequence in context: A220531 A322085 A128865 * A302113 A357510 A336028

Adjacent sequences: A269267 A269268 A269269 * A269271 A269272 A269273

KEYWORD

nonn

AUTHOR

R. H. Hardin, Feb 21 2016

STATUS

approved

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Last modified February 2 20:41 EST 2023. Contains 360024 sequences. (Running on oeis4.)