a(0) = 0; for n > 0, a(n) = sigma(n)-1.

Terms

a(0) =0a(1) =0a(2) =2a(3) =3a(4) =6a(5) =5a(6) =11a(7) =7a(8) =14a(9) =12a(10) =17a(11) =11a(12) =27a(13) =13a(14) =23a(15) =23a(16) =30a(17) =17a(18) =38a(19) =19a(20) =41a(21) =31a(22) =35a(23) =23a(24) =59a(25) =30a(26) =41a(27) =39a(28) =55a(29) =29