a(n) = (2n)! / (n-1)!.A126804a(n) = (2n)! / (n-1)!.Terms a(0) =2a(1) =24a(2) =360a(3) =6720a(4) =151200a(5) =3991680a(6) =121080960a(7) =4151347200a(8) =158789030400External referencesoeis: A126804