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A071879 G.f. satisfies: A(x) = 1 + x*A(x) + x^3*A(x)^3. 1
1, 1, 1, 2, 5, 11, 24, 57, 141, 349, 871, 2212, 5688, 14730, 38403, 100829, 266333, 706997, 1885165, 5047522, 13565203, 36578497, 98934826, 268342933, 729709432, 1989021256, 5433518806, 14873285506, 40790118487, 112064912455 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,4

COMMENTS

Number of ordered trees with n edges and having nonleaf nodes of outdegrees 1 or 3. - Emeric Deutsch, Nov 03 2002. [Comment corrected by Christian G. Bower, Sep 25 2007]

Sequence is a Motzkin-like sequence. The Motzkin sequence A001006 counts ordered trees with n edges and having nodes of outdegree 0, 1, or 2 [g.f. f(x) defined by f = 1+x*f+(x*f)^2]. - Emeric Deutsch, Sep 30 2007

G.f. (offset 1) is series reversion of x^2/(x+x^2+x^4).

LINKS

Table of n, a(n) for n=0..29.

FORMULA

a(n) = sum(C(n+1, 1+2i)*C(n-2i, i), i=0..floor(n/3))/(n+1). - Emeric Deutsch, Nov 03 2002

a(n) = sum{k=0..floor(n/3), C(n,3k)C(3k,k)/(2k+1)}; - Paul Barry, Sep 07 2006

Conjecture: 2*n*(2*n+3)*a(n) +2*(1-6*n^2)*a(n-1) +6*(2*n-1)*(n-1)*a(n-2) -31*(n-1)*(n-2)*a(n-3)=0. - R. J. Mathar, Nov 13 2012

a(n) ~ (2+3*2^(1/3))^(3/2) * (1+3*2^(-2/3))^n/(4*sqrt(6*Pi)*n^(3/2)). - Vaclav Kotesovec, Aug 19 2013

EXAMPLE

G.f.: A(x) = 1 + x + x^2 + 2*x^3 + 5*x^4 + 11*x^5 + 24*x^6 + ...

The first-order differences of the terms forms the coefficients of A(x)^3:

A(x)^3 = 1 + 3*x + 6*x^2 + 13*x^3 + 33*x^4 + 84*x^5 + 208*x^6 + 522*x^7 +...

MAPLE

a:= n-> add(binomial(n+1, 1+2*i)*binomial(n-2*i, i), i=0..floor(n/3))/(n+1): seq(a(n), n=0..29);

MATHEMATICA

a[n_] := Sum[Binomial[n+1, 1+2i]*Binomial[n-2i, i], {i, 0, Floor[n/3]}]/(n+1);

PROG

(PARI) a(n)=if(n<0, 0, polcoeff(serreverse(x^2/(x+x^2+x^4+x^2*O(x^n))), n+1))

(PARI) Vec(serreverse(x/(1+x+x^3)+O(x^66))/x) /* Joerg Arndt, Aug 19 2012 */

CROSSREFS

Sequence in context: A110513 A018115 A018007 * A228862 A134527 A124379

Adjacent sequences:  A071876 A071877 A071878 * A071880 A071881 A071882

KEYWORD

nonn

AUTHOR

Paul D. Hanna, Jun 10 2002

EXTENSIONS

Name changed by Paul D. Hanna, Nov 15 2012

STATUS

approved

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Last modified April 25 03:36 EDT 2014. Contains 240994 sequences.