Olympiad Maths Prep

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Number theory Difficulty 4.5 AIME Find the answer Romania

How many three-digit primes can be turned into perfect cubes with a permutation of their digits?

Solution

The three-digit perfect cubes are 125125, 216216, 343343, 512512 and 729729. The primes must end with an odd digit, different from 55, and must be not divisible by 33. Therefore we must consider only 251251, 521521, 433433. All of them are primes.

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