a(n) = 120*(3*n)!/(n!*(n+2)!^2).

Terms

a(0) =30a(1) =20a(2) =75a(3) =504a(4) =4620a(5) =51480a(6) =656370a(7) =9237800a(8) =140229804a(9) =2259901800a(10) =38230005450a(11) =673210036800