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

Terms

a(0) =1a(1) =3a(2) =7a(3) =49a(4) =121a(5) =2521a(6) =5041a(7) =208321a(8) =907201a(9) =32810401a(10) =39916801a(11) =10621860481a(12) =6227020801