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

Terms

a(0) =1a(1) =1a(2) =1a(3) =5a(4) =1a(5) =17a(6) =1a(7) =49a(8) =28a(9) =129a(10) =1a(11) =564a(12) =1a(13) =769a(14) =1459a(15) =2049a(16) =1a(17) =11387a(18) =1a(19) =13313a(20) =32806a(21) =20481a(22) =1a(23) =223798a(24) =3126a(25) =98305a(26) =551125a(27) =540673a(28) =1a(29) =2662642