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

Terms

a(0) =1a(1) =3a(2) =8a(3) =36a(4) =144a(5) =1010a(6) =5760a(7) =50400a(8) =416640a(9) =4250232a(10) =43545600a(11) =553106400a(12) =6706022400a(13) =95865541200