Oh! a+b+c+d+e+f+g+h+i is 3*magic sum=3*1999=0 mod (3), but I proved earlier that a+b+c+d+e+f+g+h+i=1 (mod 3), so contradiction and 1999 cannot be the magic sum. (In fact, only integers, positive and negative, that are congruent to 0 mod 3 can be the magic sum)

Thanks!

Tina Jin