OFFSET
0,3
LINKS
Andrew Howroyd, Table of n, a(n) for n = 0..200
M. Dziemianczuk, Enumerations of plane trees with multiple edges and Raney lattice paths, Discrete Mathematics 337 (2014): 9-24.
FORMULA
a(n) = Sum_{k=1..n+1} Sum_{i=1..k-1} Sum_{j=0..floor((n-i)/4)} (-1)^j*binomial(k, i)*binomial(i, j)*binomial(n-i, k-i-1)*binomial(n-4*j-1, i-1)/k for n > 0. - Andrew Howroyd, Feb 24 2020
PROG
(PARI) a(n)={my(m=4); if(n<1, n==0, sum(k=1, n+1, sum(i=1, k-1, sum(j=0, (n-i)\m, (-1)^j*binomial(k, i)*binomial(i, j)*binomial(n-i, k-i-1)*binomial(n-m*j-1, i-1)))/k))} \\ Andrew Howroyd, Feb 24 2020
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Sep 14 2014
EXTENSIONS
Terms a(11) and beyond from Andrew Howroyd, Feb 24 2020
STATUS
approved