a(n) = Sum_{d|n} phi(n/d)^d, where phi = Euler totient function (A000010).

Terms

a(0) =1a(1) =2a(2) =3a(3) =4a(4) =5a(5) =8a(6) =7a(7) =10a(8) =15a(9) =22a(10) =11a(11) =34a(12) =13a(13) =44a(14) =105a(15) =42a(16) =17a(17) =116a(18) =19a(19) =314a(20) =357a(21) =112a(22) =23a(23) =426a(24) =1045a(25) =158a(26) =747a(27) =1474a(28) =29a(29) =5290