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

Terms

a(0) =0a(1) =0a(2) =-2a(3) =3a(4) =0a(5) =-3a(6) =-7a(7) =16a(8) =2a(9) =-15a(10) =-21a(11) =31a(12) =24a(13) =-15a(14) =-57a(15) =34a(16) =25a(17) =-17a(18) =-27a(19) =77a(20) =8a(21) =-99a(22) =-111a(23) =155a(24) =117a(25) =-36a(26) =-140a(27) =40a(28) =25a(29) =-80