a(n) = Sum_{d|n} d^(d').

Terms

a(0) =1a(1) =3a(2) =4a(3) =259a(4) =6a(5) =7782a(6) =8a(7) =68719476995a(8) =531445a(9) =10000008a(10) =12a(12) =14a(13) =20661046794a(14) =2562890634a(16) =18a(18) =20