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A000014
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Number of series-reduced trees with n nodes.
(Formerly M0320 N0118)
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20
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0, 1, 1, 0, 1, 1, 2, 2, 4, 5, 10, 14, 26, 42, 78, 132, 249, 445, 842, 1561, 2988, 5671, 10981, 21209, 41472, 81181, 160176, 316749, 629933, 1256070, 2515169, 5049816, 10172638, 20543579, 41602425, 84440886, 171794492, 350238175, 715497037, 1464407113
(list;
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listen;
history;
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OFFSET
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0,7
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REFERENCES
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F. Bergeron, G. Labelle and P. Leroux, Combinatorial Species and Tree-Like Structures, Camb. 1998, p. 284.
D. G. Cantor, personal communication.
F. Harary, Graph Theory. Addison-Wesley, Reading, MA, 1969, p. 232.
F. Harary and E. M. Palmer, Graphical Enumeration, Academic Press, NY, 1973, p. 62, Fig. 3.3.3.
F. Harary and G. Prins, The number of homeomorphically irreducible trees and other species, Acta Math., 101 (1959), 141-162.
F. Harary, R. W. Robinson and A. J. Schwenk, Twenty-step algorithm for determining the asymptotic number of trees of various species, J. Austral. Math. Soc., Series A, 20 (1975), 483-503. Errata: Vol. A 41 (1986), p. 325.
J. L. Gross and J. Yellen, eds., Handbook of Graph Theory, CRC Press, 2004; p. 526.
N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
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LINKS
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Christian G. Bower, Table of n, a(n) for n = 0..500
N. J. A. Sloane, Illustration of initial terms
Eric Weisstein's World of Mathematics, Series-Reduced Tree
Index entries for sequences related to trees
Index entries for "core" sequences
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FORMULA
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G.f.: A(x) = ((x-1)/x)*f(x) + ((1+x)/x^2)*g(x) - (1/x^2)*g(x)^2 where f(x) is g.f. for A059123 and 1+g(x) is g.f. for A001678. [Harary and E. M. Palmer, p. 62, Eq. (3.3.10) with extra -(1/x^2)*Hbar(x)^2 term which should be there according to eq.(3.3.14), p. 63, with eq.(3.3.9)].
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MAPLE
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with (powseries): with (combstruct): n := 30: Order := n+3: sys := {B = Prod(C, Z), S = Set(B, 1 <= card), C = Union(Z, S)}:
G001678 := (convert(gfseries(sys, unlabeled, x) [S(x)], polynom)) * x^2: G0temp := G001678 + x^2:
G059123 := G0temp / x + G0temp - (G0temp^2+eval(G0temp, x=x^2))/(2*x):
G000014 := ((x-1)/x) * G059123 + ((1+x)/x^2) * G0temp - (1/x^2) * G0temp^2:
A000014 := 0, seq(coeff(G000014, x^i), i=1..n); # from UlrSchimke(AT)aol.com
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CROSSREFS
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Cf. A000055 (trees), A001678 (series-reduced planted trees), A007827 (series-reduced trees by leaves).
Sequence in context: A127712 A178113 A032090 * A114851 A099364 A125951
Adjacent sequences: A000011 A000012 A000013 * A000015 A000016 A000017
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KEYWORD
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nonn,easy,core,nice
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AUTHOR
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N. J. A. Sloane.
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EXTENSIONS
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G.f. corrected by Wolfdieter Lang, Jan 09 2001.
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STATUS
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approved
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