Find all pairs of prime numbers and satisfying the equality
Solution
Answer: and .
If or , then the obtained quadratic equations with respect to have two prime solutions: and .
Now let . We rewrite the initial equation in the form . Note that the greatest common divisor of the numbers and is equal to either or . Since and we see that exactly one of the numbers and can be divisible by , and so exactly one of them is divisible by . If , then ,
and if , then . In any case . Then we obtain , so , i.e. , which is impossible for . Therefore, there are no solutions different from the solutions mentioned above.
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