{a,-200,-1},{b,-200,200},{c,-200,200} + {a,1,200},{b,-200,200},{c,-200,200}
+ {a=0},{b,-200,-1},{c,-200,200} + {a=0},{b,1,200},{c,-200,200}
+ {a=0},{b=0},{c,-200,-1} + {a=0},{b=0},{c,1,200}
__________________________________________________________________ or you can
NSum[(-1)^(a+b+c)/(Sqrt[(a+b-c)^2+(-a+b+c)^2+(a-b+c)^2] + Boole[a==0&&b==0&&c==0]),{a,-200,200},{b,-200,200},{c,-200,200}] -1