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A231025
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Number of n X 2 0..2 arrays x(i,j) with each element horizontally, vertically or antidiagonally next to at least one element with value (x(i,j)+1) mod 3 and at least one element with value (x(i,j)-1) mod 3, and upper left element zero.
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1
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0, 2, 12, 62, 344, 1864, 10162, 55324, 301278, 1640592, 8933808, 48648834, 264916012, 1442593630, 7855607976, 42777519416, 232943926258, 1268490401852, 6907533179198, 37614801461920, 204830473095648, 1115399286396802
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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) = 4*a(n-1) + 8*a(n-2) - 4*a(n-4) + a(n-5).
Empirical g.f.: 2*x^2*(1 + 2*x - x^2) / (1 - 4*x - 8*x^2 + 4*x^4 - x^5). - Colin Barker, Sep 25 2018
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EXAMPLE
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Some solutions for n=3:
..0..1....0..2....0..1....0..2....0..2....0..1....0..2....0..1....0..1....0..2
..2..1....1..0....2..1....1..0....1..2....2..2....1..1....2..0....2..0....1..2
..0..2....2..1....2..0....1..2....0..1....1..0....2..0....1..2....2..1....1..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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