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

Terms

a(0) =1a(1) =2a(2) =5a(3) =10a(4) =257a(5) =50a(6) =46657a(7) =16450a(8) =1679681a(9) =327682a(10) =10000000001a(11) =4196098a(13) =15237476354