OFFSET
0,2
COMMENTS
The terms of this sequence may be computed via a determinant; see Lemma 10.7.2 of the Krattenthaler reference for details.
LINKS
Christian Krattenthaler, "Lattice path enumeration". In: Handbook of Enumerative Combinatorics. Edited by Miklos Bona. CRC Press, 2015, pages 589-678.
FORMULA
G.f.: 2 - 1 / (Sum_{n>=0} binomial(6*n,3*n) * x^n).
PROG
(PARI) seq(n)={Vec(2 - 1/(O(x*x^n) + sum(k=0, n, binomial(6*k, 3*k)*x^k)))} \\ Andrew Howroyd, Aug 25 2020
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Lucas A. Brown, Aug 24 2020
STATUS
approved