a(n) = Sum_{d|n} (-1)^(d-1) * d^(n/d-1).

Terms

a(0) =1a(1) =0a(2) =2a(3) =-2a(4) =2a(5) =-1a(6) =2a(7) =-12a(8) =11a(9) =-11a(10) =2a(11) =-27a(12) =2a(13) =-57a(14) =108a(15) =-200a(16) =2a(17) =-40a(18) =2a(19) =-653a(20) =780a(21) =-1013a(22) =2a(23) =-1177a(24) =627a(25) =-4083a(26) =6644a(27) =-11959a(28) =2a(29) =5043