a(n) = Sum_{d|n} (n/d)^(n-n/d) * binomial(d+n-2,n-1).

Terms

a(0) =1a(1) =3a(2) =7a(3) =37a(4) =71a(5) =751a(6) =925a(7) =13161a(8) =45676a(9) =262911a(10) =184757a(11) =18014557a(12) =2704157a(13) =133062875a(14) =2838201061a(15) =16907954129a(16) =601080391a(17) =830283170617a(18) =9075135301