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A181290
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The sum of the lengths of the 2-compositions of n. A 2-composition of n is a nonnegative matrix with two rows, such that each column has at least one nonzero entry and whose entries sum up to n. The length of the 2-composition is the number of columns.
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1
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0, 2, 11, 52, 227, 944, 3800, 14944, 57748, 220128, 829968, 3101376, 11502704, 42393088, 155392768, 566918144, 2059768384, 7456496128, 26905720576, 96804463616, 347386161920, 1243665567744, 4442849839104, 15840448094208
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OFFSET
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0,2
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COMMENTS
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REFERENCES
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G. Castiglione, A. Frosini, E. Munarini, A. Restivo and S. Rinaldi, Combinatorial aspects of L-convex polyominoes, European Journal of Combinatorics, 28, 2007, 1724-1741.
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LINKS
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FORMULA
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G.f.=z(2-z)(1-z)^2/(1-4z+2z^2)^2.
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MAPLE
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g := z*(1-z)^2*(2-z)/(1-4*z+2*z^2)^2: gser := series(g, z = 0, 28): seq(coeff(gser, z, n), n = 0 .. 25);
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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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