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

Terms

a(0) =1a(1) =2a(2) =4a(3) =6a(4) =126a(5) =11a(6) =16808a(7) =518a(8) =59053a(9) =1127a(10) =2357947692a(11) =1743a(13) =554633a(14) =170859504a(15) =268435974a(17) =1948628a(19) =1280001131a(23) =4586473679