a(n) = 3*n - sum of divisors of n.

Terms

a(0) =2a(1) =3a(2) =5a(3) =5a(4) =9a(5) =6a(6) =13a(7) =9a(8) =14a(9) =12a(10) =21a(11) =8a(12) =25a(13) =18a(14) =21a(15) =17a(16) =33a(17) =15a(18) =37a(19) =18a(20) =31a(21) =30a(22) =45a(23) =12a(24) =44a(25) =36a(26) =41a(27) =28a(28) =57a(29) =18