Only one solution?

How many solutions are possible for 2 distinct positive integers A A and B B such that A B = B A A^{B} = B^{A} ?

Infinite solutions. No such pair exists. 1 pair only (2 and 4) 2,4 is a pair. But there might be more.

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1 solution

Shashi M
Apr 9, 2018

2x2x2x2 = 4x4 For any distinct numbers a and b, (i) both are prime. If a^b = b^a, a| a^b => a |b^a, contradiction. (ii) one of them is a prime (as is the case with our solution pair, 2 and 4) 2 being an even prime, we arrive at 2^4 = 4^2, For any other prime (p) and non-prime numbers, p^n = n^p leads to n = p^k. or n = p*p2 *p3 and so on. This contradicts p being prime!

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