a(n) = Sum_{k=1..floor(sqrt(n))} 2^floor(n/k-k).

Terms

a(0) =0a(1) =1a(2) =2a(3) =4a(4) =9a(5) =17a(6) =34a(7) =66a(8) =132a(9) =261a(10) =521a(11) =1033a(12) =2066a(13) =4114a(14) =8226a(15) =16420a(16) =32837a(17) =65605a(18) =131209a(19) =262281a(20) =524554a(21) =1048850a(22) =2097682a(23) =4194834a(24) =8389668a(25) =16778277a(26) =33556517a(27) =67110981a(28) =134221897a(29) =268439625