a(n) = binomial(3*n,n)^2/(2*n+1).

A188681

a(n) = binomial(3*n,n)^2/(2*n+1).

Terms

    a(0) =1a(1) =3a(2) =45a(3) =1008a(4) =27225a(5) =819819a(6) =26509392a(7) =901402560a(8) =31818681873

External references