OFFSET
0,2
FORMULA
PROG
(PARI) a(n)=sum(k=0, n, binomial(2*k, k)/(k+1)*binomial(3*(n-k), n-k)/(2*(n-k)+1))
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul D. Hanna, Jun 07 2007
STATUS
approved