Wieferich prime

This article defines a property that can be evaluated for a prime number. In other words, every prime number either satisfies this property or does not satisfy this property.
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Definition

A Wieferich prime is an odd prime $p$ such that:

$2^{p-1}\equiv 1{\pmod {p^{2}}}$.

In particular, $2$ is not a primitive root modulo a Wieferich prime.