a(n) = Sum_{ d divides n, d==1 mod 4} d - Sum_{ d divides n, d==3 mod 4} d.

Terms

a(0) =1a(1) =1a(2) =-2a(3) =1a(4) =6a(5) =-2a(6) =-6a(7) =1a(8) =7a(9) =6a(10) =-10a(11) =-2a(12) =14a(13) =-6a(14) =-12a(15) =1a(16) =18a(17) =7a(18) =-18a(19) =6a(20) =12a(21) =-10a(22) =-22a(23) =-2a(24) =31a(25) =14a(26) =-20a(27) =-6a(28) =30a(29) =-12