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A268803 Number of n X 2 0..2 arrays with some element plus some horizontally, vertically or antidiagonally adjacent neighbor totalling two not more than once. 1
9, 34, 104, 290, 772, 1972, 4914, 12010, 28922, 68836, 162274, 379524, 881712, 2036734, 4681646, 10714994, 24430816, 55516546, 125777028, 284188780, 640549034, 1440572818, 3233256010, 7243375068, 16199546178, 36172883716 (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) + 3*a(n-2) - 2*a(n-3) - 6*a(n-4) - 4*a(n-5) - a(n-6) for n>7.

Empirical g.f.: x*(9 + 16*x + 9*x^2 - 2*x^3 + 2*x^4 + 6*x^5 + 3*x^6) / (1 - x - 2*x^2 - x^3)^2. - Colin Barker, Jan 15 2019

EXAMPLE

Some solutions for n=4:

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

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

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

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

CROSSREFS

Column 2 of A268809.

Sequence in context: A000441 A067989 A002881 * A250652 A005344 A250763

Adjacent sequences:  A268800 A268801 A268802 * A268804 A268805 A268806

KEYWORD

nonn

AUTHOR

R. H. Hardin, Feb 13 2016

STATUS

approved

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Last modified September 20 07:21 EDT 2020. Contains 337264 sequences. (Running on oeis4.)