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

Terms

a(0) =1a(1) =2a(2) =4a(3) =6a(4) =126a(5) =14a(6) =16808a(7) =522a(8) =59059a(9) =2002a(10) =2357947692a(11) =1766a(13) =1075650a(14) =170862766a(15) =268439570a(17) =3779174a(19) =1280016022a(23) =4586499146