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A268792
Number of n X 2 0..2 arrays with some element plus some horizontally, vertically or antidiagonally adjacent neighbor totalling two exactly once.
1
3, 22, 78, 234, 652, 1714, 4360, 10820, 26366, 63346, 150482, 354196, 827310, 1919884, 4430664, 10175910, 23272918, 53029498, 120435100, 272714858, 615904208, 1387638220, 3119557838, 6999162874, 15675003042, 35046218020
OFFSET
1,1
LINKS
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*(3 + 16*x + 25*x^2 + 18*x^3 + 12*x^4 + 8*x^5 + 3*x^6) / (1 - x - 2*x^2 - x^3)^2. - Colin Barker, Jan 15 2019
EXAMPLE
Some solutions for n=4:
..2..1. .0..0. .1..2. .0..0. .0..2. .2..2. .2..0. .0..0. .0..1. .1..2
..0..0. .1..1. .2..1. .0..1. .1..2. .1..2. .1..0. .0..1. .0..0. .2..2
..0..0. .0..0. .1..0. .2..2. .2..2. .2..2. .0..0. .0..0. .0..1. .2..1
..0..0. .0..0. .0..1. .2..1. .2..1. .1..1. .0..1. .1..2. .1..0. .2..1
CROSSREFS
Column 2 of A268798.
Sequence in context: A178492 A005288 A143166 * A055550 A075204 A106150
KEYWORD
nonn
AUTHOR
R. H. Hardin, Feb 13 2016
STATUS
approved