a(n) = n! - (n-2)!.

Terms

a(0) =1a(1) =5a(2) =22a(3) =114a(4) =696a(5) =4920a(6) =39600a(7) =357840a(8) =3588480a(9) =39553920a(10) =475372800a(11) =6187104000a(12) =86699289600