a(n) = Sum_{k=1..n} k^floor(n/k).

Terms

a(0) =1a(1) =3a(2) =6a(3) =12a(4) =17a(5) =33a(6) =40a(7) =68a(8) =95a(9) =141a(10) =152a(11) =328a(12) =341a(13) =461a(14) =738a(15) =1130a(16) =1147a(17) =2159a(18) =2178a(19) =4068a(20) =5841a(21) =6997a(22) =7020a(23) =18198a(24) =20723a(25) =25001a(26) =38798a(27) =61546a(28) =61575a(29) =137445