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 A014535 B-trees of order 3 with n leaves. 11
 0, 1, 1, 1, 1, 2, 2, 3, 4, 5, 8, 14, 23, 32, 43, 63, 97, 149, 224, 332, 489, 727, 1116, 1776, 2897, 4782, 7895, 12909, 20752, 32670, 50426, 76767, 116206, 176289, 269615, 416774, 650647, 1023035, 1614864, 2551783, 4028217, 6344749, 9966479, 15614300, 24407844 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,6 COMMENTS A B-tree of order m is an ordered tree such that every node has at most m children, the root has at least 2 children, every node except for the root has 0 or at least m/2 children, all end-nodes are at the same level. Limit n->infinity a(n)^(1/n) = (1+sqrt(5))/2, for more detailed asymptotics see Odlyzko 1982 reference. - Vaclav Kotesovec, Jul 29 2014 REFERENCES Steven R. Finch, Mathematical Constants, Cambridge University Press, 2003, Section 5.6 Otter's tree enumeration constants, p. 311. LINKS Alois P. Heinz, Table of n, a(n) for n = 0..1000 Ph. Flajolet and A. Odlyzko, Singularity analysis of generating functions, SIAM J. Discrete Math., vol 3 (1990) pp. 216-240. See p. 20. P. Flajolet and R. Sedgewick, Analytic Combinatorics, 2009; see page 91 A. M. Odlyzko, Periodic oscillations of coefficients of power series that satisfy functional equations, Advances in Mathematics, Volume 44, Issue 2, May 1982, pp. 180-205. F. Ruskey, Information on B-Trees Eric Weisstein's World of Mathematics, B-Tree. FORMULA G.f. satisfies A(x) = x + A(x^2+x^3). a(0) = 0, a(1) = 1, a(n) = sum_{k=ceiling(n/3)..floor(n/2)} binomial(k, 3*k - n)*a(k) - Jean-François Alcover, Jul 29 2014, after Steven Finch. MAPLE spec := [ B, {B=Union(Z, Subst(M, B)), M=Union(Prod(Z, Z), Prod(Z, Z, Z))} ]: seq(combstruct[count](spec, size=n), n=0..36); # Paul Zimmermann MATHEMATICA terms = 45; A[_] = 0; Do[A[x_] = x + A[x^2 + x^3] + O[x]^terms // Normal, terms]; CoefficientList[A[x], x] (* Jean-François Alcover, Oct 23 2012, from g.f., updated Jan 10 2018 *) a = 0; a = 1; a[n_] := a[n] = Sum[Binomial[k, 3*k - n]*a[k], {k, Ceiling[n/3], Floor[n/2]}]; Table[a[n], {n, 0, 100}] (* Jean-François Alcover, Jul 29 2014 *) CROSSREFS Sequence in context: A100483 A182613 A184259 * A210642 A263140 A205006 Adjacent sequences:  A014532 A014533 A014534 * A014536 A014537 A014538 KEYWORD nonn AUTHOR STATUS approved

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Last modified June 25 10:10 EDT 2019. Contains 324351 sequences. (Running on oeis4.)