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

A370055

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

Terms

    a(0) =1a(1) =3a(2) =24a(3) =330a(4) =6552a(5) =171360a(6) =5581440a(7) =218045520a(8) =9945936000a(9) =519177859200

External references