OFFSET
0,2
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..300
SeoungJi Hong and SeungKyung Park, Hybrid d-ary trees and their generalization, Bull. Korean Math. Soc. 51 (2014), No. 1, pp. 229-235
FORMULA
a(n) = 1/(7*n+1) * Sum_{i=0..n} C(7*n+i,i)*C(7*n+i+1,n-i).
a(n) = [x^n] ((1+x)/(1-x-x^2))^(7*n+1) / (7*n+1).
G.f. satisfies: A(x) = (1+x*A(x)^7) * (1+x*A(x)^8).
MAPLE
a:= n-> add(binomial(7*n+i, i)*binomial(7*n+i+1, n-i), i=0..n)/(7*n+1):
seq(a(n), n=0..20);
CROSSREFS
KEYWORD
nonn
AUTHOR
Alois P. Heinz, Jul 10 2014
STATUS
approved