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
Math Confidence by Robin the Math Lady 
9+25+49 does not equal 81
oh many thank yous for catching that
eek
it is supposed to read
3^3 + 5^1 + 7^2 =
27 + 5 + 49 = 81