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

Terms

a(0) =1a(1) =3a(2) =6a(3) =9a(4) =13a(5) =16a(6) =21a(7) =24a(8) =29a(9) =33a(10) =38a(11) =41a(12) =48a(13) =51a(14) =56a(15) =61a(16) =67a(17) =70a(18) =77a(19) =80a(20) =87a(21) =92a(22) =97a(23) =100a(24) =109a(25) =113a(26) =118a(27) =123a(28) =130a(29) =133