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A201372
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Number of n X 5 0..1 arrays with rows and columns lexicographically nondecreasing read forwards, and nonincreasing read backwards.
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1
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2, 6, 22, 80, 268, 786, 2016, 4608, 9582, 18446, 33330, 57136, 93704, 147994, 226284, 336384, 487866, 692310, 963566, 1318032, 1774948, 2356706, 3089176, 4002048, 5129190, 6509022, 8184906, 10205552, 12625440, 15505258, 18912356, 22921216
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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) = (1/45)*n^6 - (1/60)*n^5 - (4/9)*n^4 + (11/4)*n^3 - (206/45)*n^2 + (64/15)*n.
G.f.: 2*x*(1 - 4*x + 11*x^2 - 9*x^3 + 15*x^4 - 6*x^5) / (1 - x)^7.
a(n) = 7*a(n-1) - 21*a(n-2) + 35*a(n-3) - 35*a(n-4) + 21*a(n-5) - 7*a(n-6) + a(n-7) for n>7.
(End)
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EXAMPLE
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Some solutions for n=6:
..0..1..1..1..1....0..0..0..1..1....0..0..0..1..1....0..0..0..1..1
..0..1..1..1..1....0..0..1..0..1....0..0..1..0..1....0..0..0..1..1
..0..1..1..1..1....0..1..1..1..0....0..1..0..1..0....0..1..1..0..1
..1..0..1..1..1....1..0..1..0..0....0..1..1..0..0....0..1..1..1..0
..1..1..0..0..1....1..1..0..0..0....0..1..1..0..0....1..0..1..1..0
..1..1..1..1..0....1..1..0..0..0....1..0..0..0..0....1..1..0..0..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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