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A081321 a(n) = (2/3)*(2*n+1)*(2*n-1)!*binomial(3*n,2*n). 1
6, 300, 47040, 14968800, 7991343360, 6422134118400, 7240779786240000, 10899907851216384000, 21115899915689779200000, 51167604130438090014720000, 151615591667542267763097600000, 539306547534817468755148800000000, 2267795648217238975260881584128000000 (list; graph; refs; listen; history; text; internal format)
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

MAPLE

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

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

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Last modified June 26 20:30 EDT 2019. Contains 324380 sequences. (Running on oeis4.)