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

Terms

a(0) =0a(1) =3a(2) =16a(3) =90a(4) =576a(5) =4200a(6) =34560a(7) =317520a(8) =3225600a(9) =35925120a(10) =435456000a(11) =5708102400a(12) =80472268800