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Weekly Problem 35 - 2006

Stage: 3 Challenge Level: Challenge Level:1
105

If 21 and 35 are factors of the number, then 3, 5 and 7 must all be included amongst its prime factors. This means that the required number must be a multiple of 105 and, as the complete list of factors of 105 is 1, 3, 5, 7, 15, 21, 35 and 105, the answer is 105.

This problem is taken from the UKMT Mathematical Challenges.

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