A081321 a(n) = (2/3)*(2*n+1)*(2*n-1)!*binomial(3*n,2*n).

6, 300, 47040, 14968800, 7991343360, 6422134118400, 7240779786240000, 10899907851216384000, 21115899915689779200000, 51167604130438090014720000, 151615591667542267763097600000, 539306547534817468755148800000000, 2267795648217238975260881584128000000

Offset

1,1

Links

Robert Israel, Table of n, a(n) for n = 1..194

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

Formula

(27*n^4+27*n^3+6*n^2)*a(n)+(108*n^4+648*n^3+1373*n^2+1233*n+400)*a(n+1)+(-4*n^2-12*n-8)*a(n+2) = 0. - Robert Israel, Mar 29 2017

a(n) = (2n+1)(3n-1)!/n!. - Jean-François Alcover, Sep 22 2019

Maple

seq(2/3*(2*n+1)*(2*n-1)!*binomial(3*n, 2*n), n=1..30); # Robert Israel, Mar 29 2017

Mathematica

a[n_] := (2n+1)(3n-1)!/n!;
Array[a, 30] (* Jean-François Alcover, Sep 22 2019 *)

Crossrefs

Sequence in context: A066718 A065947 A277168 * A159494 A221850 A229148

Adjacent sequences: A081318 A081319 A081320 * A081322 A081323 A081324

Keyword

nonn

Author

N. J. A. Sloane, May 22 2003

Status

approved