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A252924
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Number of n X 2 nonnegative integer arrays with upper left 0 and lower right n+2-6 and value increasing by 0 or 1 with every step right or down.
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2
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0, 0, 0, 1, 19, 120, 483, 1500, 3923, 9069, 19095, 37356, 68860, 120835, 203424, 330525, 520794, 798830, 1196562, 1754859, 2525385, 3572722, 4976785, 6835554, 9268149, 12418275, 16458065, 21592350, 28063386, 36156069, 46203670, 58594123
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OFFSET
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1,5
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COMMENTS
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LINKS
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FORMULA
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Empirical: a(n) = (1/40320)*n^8 + (1/1120)*n^7 + (7/2880)*n^6 - (1/16)*n^5 + (647/5760)*n^4 + (87/160)*n^3 - (21317/10080)*n^2 + (141/56)*n - 1.
Empirical: G.f.: x^4*(-1-10*x+15*x^2-3*x^3-3*x^4+x^5) / (x-1)^9 . - R. J. Mathar, Nov 21 2015
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EXAMPLE
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Some solutions for n=6:
..0..0....0..0....0..1....0..0....0..0....0..1....0..0....0..0....0..1....0..0
..0..1....1..1....1..1....1..1....0..0....0..1....0..1....0..0....0..1....1..1
..1..1....1..1....1..1....2..2....1..1....0..1....0..1....0..1....0..1....1..1
..1..1....1..1....1..2....2..2....1..1....0..1....1..1....1..1....0..1....1..2
..1..2....1..1....2..2....2..2....1..2....0..1....1..1....1..1....1..1....2..2
..2..2....1..2....2..2....2..2....1..2....1..2....2..2....1..2....1..2....2..2
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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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