a(n) = sigma(n), the sum of the divisors of n. Also called sigma_1(n).

Terms

a(0) =1a(1) =3a(2) =4a(3) =7a(4) =6a(5) =12a(6) =8a(7) =15a(8) =13a(9) =18a(10) =12a(11) =28a(12) =14a(13) =24a(14) =24a(15) =31a(16) =18a(17) =39a(18) =20a(19) =42a(20) =32a(21) =36a(22) =24a(23) =60a(24) =31a(25) =42a(26) =40a(27) =56a(28) =30a(29) =72