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Search: id:A000554
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| A000554 |
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Number of labeled trees of diameter 3 with n nodes.
(Formerly M4843 N2070)
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+0
1
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| 12, 60, 210, 630, 1736, 4536, 11430, 28050, 67452, 159588, 372554, 859950, 1965840, 4456176, 10026702, 22412970, 49806980, 110100060, 242220594, 530578950, 1157627352, 2516581800, 5452594550, 11777604930, 25367149836, 54492396756
(list; graph; listen)
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OFFSET
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4,1
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REFERENCES
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J. Riordan, Enumeration of trees by height and diameter, IBM J. Res. Dev. 4 (1960), 473-478.
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LINKS
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Index entries for sequences related to trees
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FORMULA
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a(n) = n(n-1)*S2(n-2, 2) where S2(n, k) denotes the Stirling numbers of 2nd kind -Victor Adamchik (adamchik(AT)cs.cmu.edu), Jul 19 2001
a(n) = n(n-1) * 2^(n-3) = 2*A000217(n-1)*A000225(n-3) - Robert G. Wilson v (rgwv(AT)rgwv.com), Jul 01 2007
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MATHEMATICA
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f[n_] := n (n - 1)*StirlingS2[n - 2, 2]; Table[ f@n, {n, 4, 29}] - Robert G. Wilson v (rgwv(AT)rgwv.com), Jul 01 2007
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CROSSREFS
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Sequence in context: A112415 A061624 A004302 this_sequence A012289 A012583 A009049
Adjacent sequences: A000551 A000552 A000553 this_sequence A000555 A000556 A000557
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KEYWORD
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nonn
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AUTHOR
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njas
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EXTENSIONS
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More terms from Robert G. Wilson v (rgwv(AT)rgwv.com), Jul 01 2007
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