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

Terms

a(0) =0a(1) =1a(2) =2a(3) =4a(4) =5a(5) =8a(6) =9a(7) =12a(8) =14a(9) =17a(10) =18a(11) =23a(12) =24a(13) =27a(14) =30a(15) =34a(16) =35a(17) =40a(18) =41a(19) =46a(20) =49a(21) =52a(22) =53a(23) =60a(24) =62a(25) =65a(26) =68a(27) =73a(28) =74a(29) =81