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

Terms

a(0) =1a(1) =3a(2) =4a(3) =29a(4) =6a(5) =1027a(6) =8a(7) =26889a(8) =272170a(9) =861851a(10) =12a(11) =515592013a(12) =14a(13) =1530809295a(14) =668366899216a(16) =18a(18) =20a(22) =24