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

Terms

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