Jacobi (or Kronecker) symbol (-1/n).

Terms

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