(6-1)^2=36-12+1 (6-1)^3=(36-12+1)(6-1) ......... only the last number 1or -1 is not a multiple of 3, when x is even, (-1)^x will be 1, then plus the last 1, 2 can not be divided by 3. when x is odd, (-1)^x will be -1, then plus the last 1, equals 0. And all the order number will be multiple of 3. Thus it can be divided by 3.