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

Terms

a(0) =1a(1) =3a(2) =11a(3) =74a(4) =629a(5) =8085a(6) =117655a(7) =2113796a(8) =43059849a(9) =1001955177a(10) =25937424611a(11) =743379914746