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

Terms

a(0) =-1a(1) =0a(2) =-4a(3) =1a(4) =-5a(5) =-1a(6) =-9a(7) =4a(8) =-9a(9) =-3a(10) =-15a(11) =5a(12) =-9a(13) =-1a(14) =-25a(15) =4a(16) =-14a(17) =-1a(18) =-21a(19) =9a(20) =-23a(21) =-11a(22) =-35a(23) =17a(24) =-14a(25) =0a(26) =-40a(27) =0a(28) =-30a(29) =-6