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

Terms

a(0) =1a(1) =2a(2) =3a(3) =5a(4) =5a(5) =13a(6) =7a(7) =21a(8) =25a(9) =41a(10) =11a(11) =135a(12) =13a(13) =113a(14) =271a(15) =297a(16) =17a(17) =875a(18) =19a(19) =1573a(20) =1765a(21) =1145a(22) =23a(23) =9215a(24) =2521a(25) =4265a(26) =13627a(27) =18539a(28) =29a(29) =71371