a(n) = (n-1)! * sigma(n).

Terms

a(0) =1a(1) =3a(2) =8a(3) =42a(4) =144a(5) =1440a(6) =5760a(7) =75600a(8) =524160a(9) =6531840a(10) =43545600a(11) =1117670400a(12) =6706022400a(13) =149448499200