Find the smallest positive integer for which there exists three pairwise distinct positive integers , such that and is a perfect cube.
Solution
Let be the required minimum value, and pairwise distinct, such that and , where .
If are all odd, then . If , then , which leads to , which isn't a perfect square. Consequently, .
Suppose now that not all the numbers have the same parity. WLOG, suppose that and have the same parity. It follows that is even and and are both odd. Then , so , which implies . Since and are odd, it follows that , so .
If , then and , and also must be a perfect cube, so . Since , it follows that , a contradiction.
Consequently, . Notice that for we may consider , for which , so the required minimum value is .
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