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

Terms

a(0) =1a(1) =2a(2) =2a(3) =8a(4) =2a(5) =122a(6) =2a(7) =1682a(8) =10082a(9) =30242a(10) =2a(11) =7318082a(12) =2a(13) =17297282a(14) =3632428802a(15) =36843206402a(16) =2a(18) =2a(22) =2