Determine the number of non-negative integers with the following property: There exists an integer exponent with such that is a divisor of .
Solution
It is obvious that and must be relatively prime. If and both hold, so does for . From , we see that implies that there exists a divisor of with . Since and (where and are both prime), the only possible exponents with of interest to us are , , and . We need therefore only consider the exponents and . Since automatically implies we only require the rests and modulo . Since holds for all odd values of , the values of with the required property are exactly the numbers and . Since and , only and are possible, and the required number of integers is equal to .
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