a(n) = Sum_{d|n} Kronecker(-1, d).

Terms

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