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

Terms

a(0) =1a(1) =2a(2) =2a(3) =3a(4) =2a(5) =11a(6) =2a(7) =19a(8) =66a(9) =1027a(10) =2a(11) =835a(12) =2a(13) =279939a(14) =1052674a(15) =69635a(16) =2a(17) =10114563a(18) =2a(19) =1074855939a(20) =78364426242a(21) =100000000003a(22) =2a(23) =4315152387a(28) =2a(30) =2