Dedekind psi function: n * Product_{p|n, p prime} (1 + 1/p).

Terms

a(0) =1a(1) =3a(2) =4a(3) =6a(4) =6a(5) =12a(6) =8a(7) =12a(8) =12a(9) =18a(10) =12a(11) =24a(12) =14a(13) =24a(14) =24a(15) =24a(16) =18a(17) =36a(18) =20a(19) =36a(20) =32a(21) =36a(22) =24a(23) =48a(24) =30a(25) =42a(26) =36a(27) =48a(28) =30a(29) =72