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

Terms

a(0) =1a(1) =3a(2) =7a(3) =49a(4) =121a(5) =2281a(6) =5041a(7) =134401a(8) =907201a(9) =13184641a(10) =39916801a(11) =3753509761a(12) =6227020801a(13) =393409336321