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

A199748

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

Terms

    a(0) =1a(1) =1a(2) =10a(3) =220a(4) =7315a(5) =324632a(6) =18009460a(7) =1198774720a(8) =93080887185

External references