[Math] Is the smallest primitive root modulo p a primitive root modulo p^2

nt.number-theoryprimitive-roots

Let $p \ne 2$ be a prime and $a$ the smallest positive integer that is a primitive root modulo $p$. Is $a$ necessarily a primitive root modulo $p^2$ (and hence modulo all powers of $p$)? I checked this for all $p < 3 \times 10^5$ and it seems to work, but I can't see any sound theoretical reason why it should be the case. What is there to stop the Teichmuller lifts of the elements of $\mathbb{F}_p^\times$ being really small?

Best Answer

It is not true in general. See http://primes.utm.edu/curios/page.php/40487.html for the example, 5 mod 40487^2.

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