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SAMC

Saudi Arabia number theory

Problem

Find all primes for which is a perfect cube.
Solution
Write the equation as Because , divides so and , for some positive integer . It follows that and consider the following cases:

Case 1. If , then not possible.

Case 2. If , then not possible.

Therefore , hence . This implies that is . It follows and .
Final answer
19

Techniques

Factorization techniquesPrime numbersTechniques: modulo, size analysis, order analysis, inequalitiesPolynomial operations