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

Terms

a(0) =1a(1) =3a(2) =8a(3) =54a(4) =144a(5) =2880a(6) =5760a(7) =206640a(8) =1491840a(9) =24675840a(10) =43545600a(11) =10298534400a(12) =6706022400