a(n) = Sum_{d|n} d^tau(n/d).

Terms

a(0) =1a(1) =3a(2) =4a(3) =9a(4) =6a(5) =20a(6) =8a(7) =33a(8) =19a(9) =40a(10) =12a(11) =108a(12) =14a(13) =68a(14) =50a(15) =161a(16) =18a(17) =225a(18) =20a(19) =278a(20) =80a(21) =148a(22) =24a(23) =850a(24) =51a(25) =200a(26) =136a(27) =600a(28) =30a(29) =1114