a(n) = Sum_{k=1..n} k^gcd(k,n).

Terms

a(0) =1a(1) =5a(2) =30a(3) =264a(4) =3135a(5) =46709a(6) =823564a(7) =16777528a(8) =387420759a(9) =10000003265a(10) =285311670666