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

Terms

a(0) =1a(1) =2a(2) =5a(3) =10a(4) =257a(5) =66a(6) =46657a(7) =16514a(8) =1679873a(9) =524290a(10) =10000000001a(11) =4200450a(13) =26121388034