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

Terms

a(0) =1a(1) =5a(2) =19a(3) =121a(4) =601a(5) =5641a(6) =35281a(7) =406561a(8) =3447361a(9) =45420481a(10) =439084801a(11) =7565564161a(12) =80951270401