Brain Teaser Solution September 2015

Q: Find positive integers A, B and C such that 3^A + 5^B + 7^C (3 to the A power + 5 to the B power + 7 to the C) is a perfect square.  What is the smallest perfect square possible?

A: 81 is the smallest perfect square possible

List the powers of 3 5 and 7

3 9 27

5 25 125

7 49 343

If we combine 9 + 25 + 49 = 81

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