OFFSET
0,2
COMMENTS
a(n) is divisible by (n+1): a(n)/(n+1) = A121677(n).
FORMULA
a(n) = Sum_{k=0..n+1} C(n+1,k) * C((n-1)*k,n-k).
EXAMPLE
At n=4, a(4) = [x^4] (1 + x*(1+x)^3 )^5 = 250, since
(1 + x*(1+x)^3 )^5 = 1 + 5*x + 25*x^2 + 85*x^3 + 250*x^4 +...
PROG
(PARI) a(n)=sum(k=0, n+1, binomial(n+1, k)*binomial((n-1)*k, n-k))
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul D. Hanna, Aug 15 2006
STATUS
approved