Find all pairs of positive integers

for which there exist infinitely many positive integers
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such that
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is itself an integer.
Laurentiu Panaitopol, Romania
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Find all pairs of positive integers $m,n\geq3$ for which there exist infinitely many positive integers $a$ such that $$\frac{a^m+a-1}{a^n+a^2-1}$$ is itself an integer.
Laurentiu Panaitopol, Romania