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A011270 Hybrid binary rooted trees with n nodes whose root is labeled by "n". 4
1, 1, 4, 18, 90, 481, 2690, 15547, 92124, 556664, 3417062, 21248966, 133576724, 847465593, 5419399722, 34895368578, 226050057378, 1472170887755, 9633297762870, 63305402213336, 417612181048826, 2764492667188504, 18358282050480384, 122265756020847943 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

LINKS

Alois P. Heinz, Table of n, a(n) for n = 0..500

Nancy S. S. Gu, Nelson Y. Li, and Toufik Mansour, 2-Binary trees: bijections and related issues, Discr. Math., 308 (2008), 1209-1221.

J. M. Pallo, On the listing and random generation of hybrid binary trees, International Journal of Computer Mathematics, 50, 1994, 135-145.

Index entries for reversions of series

Index entries for sequences related to rooted trees

FORMULA

G.f.: = 1+x*G(x)^2, where G(x) is g.f. for A007863.

Reversion of x - (x/(1 - x))^2 = 0, 1, -1, -2, -3, -4, -5, ... - Olivier Gérard, Jul 05 2001

a(n) = (2/(n+2))*Sum_{j=0...n} binomial(n+j+1, n+1)*binomial(n+j+2, n-j). - Vladimir Kruchinin, Dec 24 2010

G.f. A(x) satisfies: A(x) = 1/(1 - Sum_{k>=1} k*x^k*A(x)^k). - Ilya Gutkovskiy, Apr 10 2018

MAPLE

G:= proc(n) option remember; if n<=0 then 1 else convert(series(

      (x^2*G(n-1)^3 +x*G(n-1)^2 +1)/ (1-x), x=0, n+1), polynom) fi

    end:

a:= n-> coeff(1+x*G(n-1)^2, x, n):

seq(a(n), n=0..20); # Alois P. Heinz, Aug 22 2008

# second Maple program:

a:= proc(n) option remember; `if`(n<3, [1, 1, 4][n+1], (

      6*n*(210*n^2-411*n+163)*a(n-1)-4*(n-2)*(7*n-6)*(5*n-3)*a(n-2)

      +2*(n-3)*(2*n-3)*(35*n-16)*a(n-3))/(5*n*(n+1)*(35*n-51)))

    end:

seq(a(n), n=0..25); # Alois P. Heinz, May 18 2013

MATHEMATICA

a[0] = 1; a[n_] := n*HypergeometricPFQ[{1-n, n+1, n+2}, {3/2, 2}, -1/4]; Table[ a[n], {n, 0, 25}] (* Jean-François Alcover, Apr 02 2015, after Vladimir Kruchinin *)

CROSSREFS

Cf. A011272.

Sequence in context: A036749 A218760 A219305 * A269450 A206639 A172964

Adjacent sequences:  A011267 A011268 A011269 * A011271 A011272 A011273

KEYWORD

nonn

AUTHOR

pallo(AT)u-bourgogne.fr (Jean Pallo)

STATUS

approved

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Last modified October 22 22:34 EDT 2019. Contains 328335 sequences. (Running on oeis4.)