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

Terms

a(0) =1a(1) =2a(2) =17a(3) =34a(4) =4097a(5) =386a(6) =1679617a(7) =263170a(8) =60470273a(9) =20971522a(11) =67223554