a(1) = 1; a(n) = -(1/2) * Sum_{d|n, d > 1} d * (d + 1) * a(n/d).

Terms

a(0) =1a(1) =-3a(2) =-6a(3) =-1a(4) =-15a(5) =15a(6) =-28a(7) =-3a(8) =-9a(9) =35a(10) =-66a(11) =6a(12) =-91a(13) =63a(14) =60a(15) =-9a(16) =-153a(17) =27a(18) =-190a(19) =15a(20) =105a(21) =143a(22) =-276a(23) =21a(24) =-100a(25) =195a(26) =-54a(27) =28a(28) =-435a(29) =-75