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A269196
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Number of n X 3 0..3 arrays with some element plus some horizontally, diagonally or antidiagonally adjacent neighbor totalling three no more than once.
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1
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60, 1284, 25572, 471492, 8314020, 142233732, 2380537188, 39186271044, 636703584804, 10237337586180, 163189207436004, 2582623154662596, 40622651914004388, 635603382950474628, 9899530341266770020
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OFFSET
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1,1
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LINKS
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FORMULA
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Empirical: a(n) = 30*a(n-1) -237*a(n-2) +180*a(n-3) -36*a(n-4) for n>5.
Empirical g.f.: 12*x*(1 - 6*x)*(5 - 13*x + 28*x^2 - 12*x^3) / (1 - 15*x + 6*x^2)^2. - Colin Barker, Jan 20 2019
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EXAMPLE
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Some solutions for n=3:
..3..1..1. .2..3..2. .3..1..0. .1..0..1. .2..0..3. .3..3..3. .3..3..3
..3..1..0. .2..2..0. .0..0..1. .1..3..2. .2..3..2. .3..1..1. .3..3..2
..0..2..3. .2..2..2. .0..1..0. .0..0..2. .3..2..2. .1..0..1. .3..2..3
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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