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

Terms

a(0) =1a(1) =2a(2) =9a(3) =18a(4) =1025a(5) =74a(6) =279937a(7) =65554a(8) =10077705a(9) =1049602a(10) =100000000001a(11) =16777306a(13) =78364444034