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

Terms

a(0) =1a(1) =0a(2) =3a(3) =-1a(4) =2a(5) =3a(6) =6a(7) =-12a(8) =3a(9) =20a(10) =23a(11) =-49a(12) =-46a(13) =41a(14) =182a(15) =-100a(16) =-97a(17) =-6a(18) =-3a(19) =-613a(20) =418a(21) =1941a(22) =1944a(23) =-5518a(24) =-4765a(25) =1364a(26) =10205a(27) =2629a(28) =2632a(29) =-1181