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A269278
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Number of 3 X n 0..3 arrays with some element plus some horizontally or antidiagonally adjacent neighbor totalling three exactly once.
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1
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0, 1620, 46872, 1104264, 23549400, 474819408, 9230973192, 174918307032, 3252108138552, 59583135523968, 1078987217468328, 19354648265646120, 344454190256524824, 6089633274402902448, 107049250394211722184
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OFFSET
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1,2
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LINKS
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FORMULA
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Empirical: a(n) = 36*a(n-1) - 378*a(n-2) + 972*a(n-3) - 729*a(n-4) for n>7.
Empirical g.f.: 36*x^2*(45 - 318*x + 812*x^2 - 1698*x^3 + 2061*x^4 - 756*x^5) / (1 - 18*x + 27*x^2)^2. - Colin Barker, Jan 21 2019
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EXAMPLE
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Some solutions for n=3:
..2..3..1. .0..1..3. .3..2..1. .2..2..2. .1..0..0. .0..0..3. .2..0..2
..3..0..2. .3..3..0. .3..3..3. .0..0..1. .2..2..0. .0..1..3. .0..0..1
..2..0..1. .2..0..1. .2..3..1. .2..0..3. .3..0..1. .3..3..2. .3..3..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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