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A217268
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Number of n X 3 arrays of occupancy after each element moves to some horizontal or vertical neighbor.
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1
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2, 64, 1472, 33856, 772800, 17640000, 402494400, 9183772224, 209543184576, 4781079618624, 109088244863424, 2489028863068224, 56791310102324928, 1295787666826276416, 29565538631067860928, 674586660240498844224
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OFFSET
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1,1
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COMMENTS
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LINKS
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FORMULA
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Empirical: a(n) = 24*a(n-1) - 648*a(n-3) + 729*a(n-4) for n>5.
Empirical g.f.: 2*x*(1 + 8*x - 32*x^2 - 88*x^3 + 135*x^4) / ((1 - 24*x + 27*x^2)*(1 - 27*x^2)). - Colin Barker, Jul 23 2018
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EXAMPLE
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Some solutions for n=3:
..1..1..0....1..1..0....1..3..1....1..1..2....0..2..2....0..1..0....1..2..0
..2..0..1....0..1..1....1..0..0....2..0..0....0..0..0....1..2..3....1..1..1
..1..1..2....1..3..1....0..1..2....1..2..0....1..3..1....2..0..0....1..1..1
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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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