a(n) = n! + (n-1)!.

Terms

a(0) =2a(1) =3a(2) =8a(3) =30a(4) =144a(5) =840a(6) =5760a(7) =45360a(8) =403200a(9) =3991680a(10) =43545600a(11) =518918400a(12) =6706022400a(13) =93405312000