a(1) = 1; a(n) = -Sum_{k=1..n} a(k/gcd(n,k)).

Terms

a(0) =1a(1) =-2a(2) =0a(3) =-3a(4) =3a(5) =-5a(6) =5a(7) =-12a(8) =8a(9) =-12a(10) =16a(11) =-31a(12) =31a(13) =-55a(14) =23a(15) =-99a(16) =131a(17) =-184a(18) =184a(19) =-389a(20) =157a(21) =-528a(22) =760a(23) =-1171a(24) =800a(25) =-2058a(26) =1235a(27) =-3248a(28) =4442a(29) =-5566