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A266471
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Number of 4 X n binary arrays with rows and columns lexicographically nondecreasing and column sums nonincreasing.
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1
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5, 12, 29, 66, 137, 261, 463, 775, 1237, 1898, 2817, 4064, 5721, 7883, 10659, 14173, 18565, 23992, 30629, 38670, 48329, 59841, 73463, 89475, 108181, 129910, 155017, 183884, 216921, 254567, 297291, 345593, 400005, 461092, 529453, 605722, 690569
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OFFSET
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1,1
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LINKS
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FORMULA
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Empirical: a(n) = (1/120)*n^5 + (1/24)*n^4 + (17/24)*n^3 - (25/24)*n^2 + (257/60)*n + 1.
G.f.: x*(5 - 18*x + 32*x^2 - 28*x^3 + 11*x^4 - x^5) / (1 - x)^6.
a(n) = 6*a(n-1) - 15*a(n-2) + 20*a(n-3) - 15*a(n-4) + 6*a(n-5) - a(n-6) for n>6.
(End)
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EXAMPLE
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Some solutions for n=4:
..0..0..0..0....0..0..0..0....0..1..1..1....0..0..0..0....0..0..1..1
..0..0..0..0....0..0..0..0....1..0..0..0....0..0..1..1....0..1..0..0
..1..1..1..1....0..0..0..0....1..0..1..1....1..1..0..0....1..0..0..0
..1..1..1..1....1..1..1..1....1..1..0..0....1..1..1..1....1..1..1..1
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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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