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A232921 Number of 2 X n 0..2 arrays with no element x(i,j) adjacent to value 2-x(i,j) horizontally, diagonally or antidiagonally. 1
9, 18, 54, 144, 396, 1080, 2952, 8064, 22032, 60192, 164448, 449280, 1227456, 3353472, 9161856, 25030656, 68385024, 186831360, 510432768, 1394528256, 3809922048, 10408900608, 28437645312, 77693091840, 212261474304 (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) = 2*a(n-1) + 2*a(n-2).

Conjectures from Colin Barker, Oct 06 2018: (Start)

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

a(n) = (-3)*(sqrt(3)*((1-sqrt(3))^n - (1+sqrt(3))^n)) / 2.

(End)

EXAMPLE

Some solutions for n=5:

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

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

CROSSREFS

Row 2 of A232920.

Sequence in context: A086500 A022669 A107313 * A295473 A255839 A166640

Adjacent sequences:  A232918 A232919 A232920 * A232922 A232923 A232924

KEYWORD

nonn

AUTHOR

R. H. Hardin, Dec 02 2013

STATUS

approved

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Last modified September 24 23:43 EDT 2022. Contains 356951 sequences. (Running on oeis4.)