What makes a number a perfect power?

Algebra Level 1

M = 2 M = 2 is an integer that satisfies M + M = M × M M + M = M \times M .

Can we also find a positive integer M M such that M + M + + M = M × M × × M , M + M + \cdots + M = M \times M \times \cdots \times M , where the numbers of M M used in both sides of the equation are equal and greater than 2?

Yes No

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2 solutions

David Vreken
Sep 24, 2018

Let there be n > 2 n > 2 M M s on each side of the equation. Then n M = M n nM = M^n , which solves to M = n 1 n 1 M = n^{\frac{1}{n - 1}} for positive real solutions of M M .

Since n < 2 n 1 n < 2^{n - 1} for n > 2 n > 2 , we have M = n 1 n 1 < ( 2 n 1 ) 1 n 1 M = n^{\frac{1}{n - 1}} < (2^{n - 1})^{\frac{1}{n - 1}} or M < 2 M < 2 for n > 2 n > 2 .

This means that if a positive integer M M exists such that n > 2 n > 2 , M < 2 M < 2 , which means M = 1 M = 1 . However, if M = 1 M = 1 , then n M = M n nM = M^n would be n 1 = 1 n n \cdot 1 = 1^n , or n = 1 n = 1 , which cannot be true as n > 2 n > 2 .

Therefore, there are no positive integers M M such that n > 2 n > 2 .

Syed Hamza Khalid
Sep 25, 2018

There is no answer to satisfy such equations except 0 and 2. Since the question states n to be greater than 2, no solution exist

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