If you are trying to find n consecutive integers whose sum is x, and n is an odd number, then the middle number is x/n, and the other numbers go up and down by one each.

Specifically in this case, n is 3 and x is -63.  Divide -63/3 and you get -21.  So the three numbers are -22, -21, and -20.  Add them up and you get -63.