a(n) = (n-1)! * Sum_{d|n} d^(n-d+1).

Terms

a(0) =1a(1) =3a(2) =8a(3) =78a(4) =144a(5) =14400a(6) =5760a(7) =5851440a(8) =88583040a(9) =5859786240a(10) =43545600a(12) =6706022400