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

Terms

a(0) =1a(1) =2a(2) =3a(3) =4a(4) =5a(5) =20a(6) =7a(7) =38a(8) =135a(9) =4102a(10) =11a(11) =1670a(12) =13a(13) =1679624a(14) =4202505a(15) =270346a(16) =17a(17) =60539912a(18) =19a(19) =4299292682a(20) =470185508877a(22) =23a(23) =17253793802a(28) =29a(30) =31