a(0) = 1; a(n) = -Sum_{d|n} a(n-d).

Terms

a(0) =1a(1) =-1a(2) =0a(3) =-1a(4) =0a(5) =-1a(6) =1a(7) =-2a(8) =0a(9) =-2a(10) =2a(11) =-3a(12) =1a(13) =-2a(14) =2a(15) =-6a(16) =2a(17) =-3a(18) =7a(19) =-8a(20) =2a(21) =-12a(22) =12a(23) =-13a(24) =0a(25) =-3a(26) =4a(27) =-12a(28) =17a(29) =-18