a(n) = 8 * n!.

Terms

a(0) =8a(1) =16a(2) =48a(3) =192a(4) =960a(5) =5760a(6) =40320a(7) =322560a(8) =2903040a(9) =29030400a(10) =319334400a(11) =3832012800a(12) =49816166400a(13) =697426329600