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

Terms

a(0) =1a(1) =-1a(2) =9a(3) =-11a(4) =41a(5) =-87a(6) =241a(7) =-367a(8) =1185a(9) =-2207a(10) =5441a(11) =-10431a(12) =24961a(13) =-46207a(14) =124161a(15) =-218879a(16) =503297a(17) =-1028607a(18) =2319361a(19) =-4275199a(20) =10434561a(21) =-19826687a(22) =43847681a(23) =-85651455a(24) =191225857a(25) =-365699071a(26) =849625089a(27) =-1588051967a(28) =3444539393a(29) =-7070580735