In Its Prime

You may have heard that one’s not prime.
That’s not been standard all the time.
The notion comes from ancient Greeks,
Who deemed one not a number (freaks).
Some also thought all primes were odd,
Omitting two as well (how flawed).
The Middle Ages saw at last
That one’s a number; then it passed
For prime for several centuries,
Contested seldom (Euler, please),
But after 1956,
Instructors had agreed to fix
Their lists of primes to all exclude
The number one, which now is viewed
To be a “unit.” What’s the deal?
To count it now, we would repeal
The wording of a lot of rules
Most often learned in higher schools.
The sieve of Eratosthenes,
For instance, wouldn’t work with ease.
So every prime must have two factors,
Heedless of the rule’s detractors.