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

Terms

a(0) =0a(1) =1a(2) =2a(3) =4a(4) =4a(5) =9a(6) =6a(7) =12a(8) =12a(9) =17a(10) =10a(11) =28a(12) =12a(13) =25a(14) =30a(15) =32a(16) =16a(17) =45a(18) =18a(19) =52a(20) =44a(21) =41a(22) =22a(23) =76a(24) =40a(25) =49a(26) =54a(27) =76a(28) =28a(29) =105