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A269104
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Number of n X 3 0..3 arrays with some element plus some horizontally or vertically adjacent neighbor totalling three no more than once.
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1
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60, 1740, 40908, 872460, 17593092, 342055548, 6482020140, 120520189980, 2208175854948, 39988864047276, 717328864510092, 12766536225007020, 225704408971133124, 3967699804321484124, 69407066832964073964
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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) = 36*a(n-1) - 378*a(n-2) + 972*a(n-3) - 729*a(n-4) for n>5.
Empirical g.f.: 12*x*(5 - 35*x + 79*x^2 - 69*x^3 + 18*x^4) / (1 - 18*x + 27*x^2)^2. - Colin Barker, Jan 19 2019
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EXAMPLE
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Some solutions for n=3:
..1..0..2. .0..0..2. .2..3..3. .3..3..2. .2..2..3. .1..1..1. .2..3..3
..1..1..0. .0..1..3. .0..2..3. .3..2..0. .2..3..3. .0..0..0. .2..2..3
..3..2..2. .2..0..2. .0..0..0. .3..0..1. .1..3..3. .1..1..0. .0..0..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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