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A221397
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Number of n X 3 arrays of occupancy after each element moves to some horizontal, diagonal or antidiagonal neighbor, with no 2-loops and with no occupancy greater than 2.
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1
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0, 6, 30, 144, 672, 3108, 14328, 65976, 303672, 1397520, 6431136, 29594352, 136184256, 626677152, 2883768672, 13270180608, 61065117312, 281002082880, 1293081432192, 5950345861248, 27381582408576, 126001256419584
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OFFSET
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1,2
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COMMENTS
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LINKS
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FORMULA
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Empirical: a(n) = 6*a(n-1) - 6*a(n-2) -2*a(n-3).
Empirical g.f.: 6*x^2*(1 - x) / (1 - 6*x + 6*x^2 + 2*x^3). - Colin Barker, Aug 05 2018
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EXAMPLE
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Some solutions for n=3:
..0..2..0....1..2..0....0..2..0....0..2..0....1..2..0....0..2..1....0..2..1
..1..2..0....0..2..1....0..2..2....1..2..1....1..2..1....0..2..1....2..2..0
..1..2..1....0..2..1....1..2..0....1..2..0....0..2..0....1..2..0....0..2..0
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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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