a(n) = Sum_{d|n} phi(d)^(d-1).

Terms

a(0) =1a(1) =2a(2) =5a(3) =10a(4) =257a(5) =38a(6) =46657a(7) =16394a(8) =1679621a(9) =262402a(10) =10000000001a(11) =4194350a(13) =13060740674