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Search: id:A000238
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| A000238 |
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Number of oriented trees with n nodes.
(Formerly M2756 N1108)
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+0
5
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| 1, 1, 3, 8, 27, 91, 350, 1376, 5743, 24635, 108968, 492180, 2266502, 10598452, 50235931, 240872654, 1166732814, 5702001435, 28088787314, 139354922608, 695808554300, 3494390057212, 17641695461662, 89495023510876, 456009893224285, 2332997330210440
(list; graph; listen)
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OFFSET
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1,3
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REFERENCES
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N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
F. Bergeron, G. Labelle and P. Leroux, Combinatorial Species and Tree-Like Structures, Camb. 1998, p. 286.
F. Harary and E. M. Palmer, Graphical Enumeration, Academic Press, NY, 1973, p. 60, r(x).
J. Riordan, An Introduction to Combinatorial Analysis, Wiley, 1958, p. 138.
R. Simion, Trees with 1-factors and oriented trees, Discrete Math., 88 (1991), 93-104.
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LINKS
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N. J. A. Sloane, Table of n, a(n) for n = 1..350
Index entries for sequences related to trees
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FORMULA
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G.f. = x+x^2+3*x^3+8*x^4+27*x^5+... = R(x)-R(x)^2, where R(x) = g.f. for A000151.
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MAPLE
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A:= proc(n) option remember; if n=0 then 0 else unapply (convert (series (x*exp (2* add (A(n-1)(x^k)/k, k=1..n-1)), x=0, n), polynom), x) fi end: a:= n-> coeff (series (A(n+1)(x) *(1-A(n+1)(x)), x=0, n+1), x, n): seq (a(n), n=1..26); [From Alois P. Heinz (heinz(AT)hs-heilbronn.de), Aug 20 2008]
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CROSSREFS
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Sequence in context: A148839 A148840 A047153 this_sequence A148841 A148842 A148843
Adjacent sequences: A000235 A000236 A000237 this_sequence A000239 A000240 A000241
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KEYWORD
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nonn,easy,nice
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AUTHOR
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N. J. A. Sloane (njas(AT)research.att.com).
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EXTENSIONS
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2 errors corrected by Paul Zimmermann Mar 01, 1996.
More terms from N. J. A. Sloane (njas(AT)research.att.com), Mar 10 2007
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