The best way to answer this depends on how much Math you've had.

Here's one way:

If (a - b)|100 then we can say that (a - b)k = 100, where k is a positive integer.

Thus . So

<-- Singling out the first term of the summation

Now, each term in the series is divisible by at least 100 due to the factor of . But there is another 100 involved: from the , i > 0. So all terms are divisible by at least 10000.

-Dan