A076151 a(n) = (n-1)!*binomial(3*n,n)/(3*(2*n+1)).

1, 8, 110, 2184, 57120, 1860480, 72681840, 3315312000, 173059286400, 10178348544000, 666172912204800, 48032775105638400, 3783468344527872000, 323279062935013785600, 29783920485745730304000, 2943352142120754524160000, 310589942708652231905280000

Offset

2,2

Links

Table of n, a(n) for n=2..18.

Michel Bousquet and Cédric Lamathe, Enumeration of solid trees according to edge number and edge degree distribution, Discr. Math., 298 (2005), 115-141.

Formula

2*n*(2*n+1)*a(n) - 3*(n-1)*(3*n-1)*(3*n-2)*a(n-1) = 0. - R. J. Mathar, Jun 07 2013

a(n) ~ 3^(3*n-1/2) * n^(n-2) / (2^(2*n+3/2) * exp(n)). - Amiram Eldar, Sep 18 2025

Mathematica

a[n_] := (n-1)! * Binomial[3*n, n] / (3 * (2*n+1)); Array[a, 20, 2] (* Amiram Eldar, Sep 18 2025 *)

Crossrefs

Sequence in context: A380045 A098623 A297971 * A020560 A144813 A079660

Adjacent sequences: A076148 A076149 A076150 * A076152 A076153 A076154

Keyword

nonn,easy

Author

N. J. A. Sloane, May 18 2003

Status

approved