OFFSET
2,2
LINKS
Andrew Howroyd, Table of n, a(n) for n = 2..200
G. Labelle, C. Lamathe and P. Leroux, A classification of plane and planar 2-trees, arXiv:math/0202052 [math.CO], 2002.
FORMULA
a(n) = n! * (2/3 * C(n) - 1/6 * C(n+1)), where C(n) = A000108(n).
a(n) = RisingFactorial(5 + n, n) assuming offset 0. - Peter Luschny, Mar 22 2022
MATHEMATICA
a[n_]:=n! * (2/3 * CatalanNumber[n] - 1/6 * CatalanNumber[n+1]); Array[a, 50, 2] (* Stefano Spezia, Sep 01 2018 *)
PROG
(PARI) a(n)=if(n < 2, 0, n!*(4*binomial(2*n, n)/(n+1)-binomial(2*n+2, n+1)/(n+2))/6) \\ Andrew Howroyd, Aug 31 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
Ralf Stephan, Apr 22 2004
STATUS
approved