Let be a positive integer such that is a perfect cube. What is the sum of all possible values of ?
0
Step-by-Step Solution
Key idea: This is a perfect power bounding problem. For large , the expression lies strictly between consecutive cubes, so only small need checking. Modular arithmetic eliminates remaining candidates.
Step 1: Compare with nearby cubes. Note .
Our expression: .
Difference: .
For , .
Step 2: Compare with . Clearly for .
So for , . Thus cannot be a perfect cube for .
Step 3: Check : , not a cube.
Step 4: No positive integer satisfies the condition. Sum of all possible values is 0.
Step 5: Verify no edge cases missed. For (not positive), , not cube. Negative excluded by problem.
Answer: 0