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A053526
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Number of bipartite graphs with 3 edges on nodes {1..n}.
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4
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0, 0, 0, 0, 16, 110, 435, 1295, 3220, 7056, 14070, 26070, 45540, 75790, 121121, 187005, 280280, 409360, 584460, 817836, 1124040, 1520190, 2026255, 2665355, 3464076, 4452800, 5666050, 7142850, 8927100, 11067966, 13620285
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OFFSET
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0,5
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REFERENCES
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R. P. Stanley, Enumerative Combinatorics, Cambridge, Vol. 2, 1999; see Problem 5.5.
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LINKS
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Table of n, a(n) for n=0..30.
Chai Wah Wu, Graphs whose normalized Laplacian matrices are separable as density matrices in quantum mechanics, arXiv preprint arXiv:1407.5663, 2014
Index entries for linear recurrences with constant coefficients, signature (7,-21,35,-35,21,-7,1).
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FORMULA
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a(n) = (n-3)*(n-2)*(n-1)*n*(n^2+3*n+4)/48.
G.f.: x^4*(16-2*x+x^2)/(1-x)^7. [Colin Barker, May 08 2012]
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CROSSREFS
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Cf. A000217 (1 edge), A050534 (2 edges).
Sequence in context: A238171 A155871 A120668 * A107908 A177046 A234250
Adjacent sequences: A053523 A053524 A053525 * A053527 A053528 A053529
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KEYWORD
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nonn,easy
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AUTHOR
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N. J. A. Sloane, Jan 16 2000
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STATUS
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approved
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