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A274853 Number of n X 3 0..2 arrays with no element equal to any value at offset (-1,0) (0,-1) or (-2,-2) and new values introduced in order 0..2. 1
2, 9, 19, 43, 100, 233, 542, 1260, 2929, 6809, 15829, 36798, 85545, 198868, 462312, 1074745, 2498479, 5808259, 13502564, 31389653, 72972090, 169639528, 394364057, 916785205, 2131267029, 4954594734, 11518035349, 26776183608, 62247074860 (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) = 3*a(n-1) - 2*a(n-2) + a(n-3) for n>4.

Empirical g.f.: x*(2 + 3*x - 4*x^2 + 2*x^3) / (1 - 3*x + 2*x^2 - x^3). - Colin Barker, Jan 31 2019

EXAMPLE

Some solutions for n=4:

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

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

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

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

CROSSREFS

Column 3 of A274858.

Sequence in context: A173663 A294546 A135207 * A264670 A026541 A038249

Adjacent sequences:  A274850 A274851 A274852 * A274854 A274855 A274856

KEYWORD

nonn

AUTHOR

R. H. Hardin, Jul 09 2016

STATUS

approved

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Last modified September 22 16:50 EDT 2020. Contains 337291 sequences. (Running on oeis4.)