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A274798 Number of n X 3 0..2 arrays with no element equal to any value at offset (-1,-2) (-2,-1) (0,-1) or (-1,0) and new values introduced in order 0..2. 1
2, 8, 30, 112, 420, 1572, 5888, 22048, 82568, 309200, 1157904, 4336144, 16238112, 60808896, 227718752, 852767104, 3193464512, 11958969152, 44784259584, 167709263104, 628042022016, 2351908141824, 8807486941952, 32982506778880 (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) + 6*a(n-2) + 2*a(n-3).

Empirical g.f.: 2*x*(1 + x)^2 / (1 - 2*x - 6*x^2 - 2*x^3). - Colin Barker, Jan 30 2019

EXAMPLE

Some solutions for n=4:

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

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

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

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

CROSSREFS

Column 3 of A274803.

Sequence in context: A278023 A077839 A052530 * A281949 A162551 A073663

Adjacent sequences:  A274795 A274796 A274797 * A274799 A274800 A274801

KEYWORD

nonn

AUTHOR

R. H. Hardin, Jul 07 2016

STATUS

approved

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Last modified May 23 12:38 EDT 2019. Contains 323514 sequences. (Running on oeis4.)