a(n) = Sum_{d|9} phi(d)*n^(9/d).

Terms

a(0) =0a(1) =9a(2) =540a(3) =19755a(4) =262296a(5) =1953405a(6) =10078164a(7) =40354335a(8) =134218800a(9) =387422001a(10) =1000002060a(11) =2357950419a(12) =5159783880a(13) =10604503845a(14) =20661052356a(15) =38443366215a(16) =68719485024a(17) =118587886425a(18) =198359302140a(19) =322687711611a(20) =512000016120