Number of divisors of n == 1 or 7 (mod 8) minus number of divisors of n == 3 or 5 (mod 8).

Terms

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