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A225894
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Number of n X 2 binary arrays whose sum with another n X 2 binary array containing no more than a single 1 has rows and columns in lexicographically nondecreasing order.
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1
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4, 12, 33, 78, 162, 304, 527, 858, 1328, 1972, 2829, 3942, 5358, 7128, 9307, 11954, 15132, 18908, 23353, 28542, 34554, 41472, 49383, 58378, 68552, 80004, 92837, 107158, 123078, 140712, 160179, 181602, 205108, 230828, 258897, 289454, 322642
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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) = (1/6)*n^4 + (1/6)*n^3 + (4/3)*n^2 + (1/3)*n + 2.
G.f.: x*(4 - 8*x + 13*x^2 - 7*x^3 + 2*x^4) / (1 - x)^5.
a(n) = 5*a(n-1) - 10*a(n-2) + 10*a(n-3) - 5*a(n-4) + a(n-5) for n>5.
(End)
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EXAMPLE
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Some solutions for n=3:
..0..0....0..0....0..0....0..1....0..1....0..0....0..0....0..0....0..1....0..1
..1..1....0..0....0..0....1..1....0..0....1..0....0..1....0..1....1..1....1..0
..1..1....1..0....0..0....0..1....1..1....1..1....1..0....0..1....1..1....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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