For all n >= 2, Sum_{2<=k<=n, gcd(k,n)>1} a(k) = 1. a(1)=1.

Terms

a(0) =1a(1) =1a(2) =1a(3) =0a(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) =-3a(18) =1a(19) =1a(20) =1a(21) =1a(22) =1a(23) =-3a(24) =-1a(25) =3a(26) =5a(27) =-1a(28) =1a(29) =-7