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A266008
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Number of n X 4 integer arrays with each element equal to the number of horizontal and antidiagonal neighbors equal to itself.
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1
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1, 4, 4, 9, 14, 21, 44, 52, 129, 138, 361, 388, 980, 1129, 2614, 3325, 6924, 9764, 18369, 28370, 49105, 81348, 132708, 230281, 362782, 644837, 1001644, 1790932, 2785729, 4947162, 7781177, 13626564, 21772724, 37503337, 60913350, 103288269, 170189068
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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) = -a(n-1) + 3*a(n-2) + 3*a(n-3) - a(n-4).
Empirical g.f.: x*(1 + 2*x)*(1 + 3*x - x^2) / (1 + x - 3*x^2 - 3*x^3 + x^4). - Colin Barker, Jan 09 2019
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EXAMPLE
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Some solutions for n=4:
..0..2..2..0....0..2..2..0....1..1..2..2....0..2..2..1....1..1..2..2
..2..2..1..1....2..2..1..1....0..2..2..0....2..2..1..0....0..2..2..0
..0..2..2..0....0..2..2..1....1..1..2..2....0..2..2..1....0..1..2..2
..2..2..1..1....2..2..1..0....0..2..2..0....2..2..1..0....1..2..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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