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

Terms

a(0) =1a(1) =1a(2) =1a(3) =17a(4) =1a(5) =129a(6) =1a(7) =769a(8) =19684a(9) =4097a(10) =1a(11) =1614804a(12) =1a(13) =98305a(14) =86093443a(15) =4295426049a(16) =1a(17) =3876302043a(18) =1a(20) =156905298046a(21) =41943041a(22) =1a(25) =805306369a(28) =1