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

Terms

a(0) =1a(1) =3a(2) =4a(3) =261a(4) =6a(5) =7789a(6) =8a(7) =68719480841a(8) =531451a(9) =10000021a(10) =12a(12) =14a(13) =20661046813a(14) =2562890656a(16) =18a(18) =20