Trey Jones wrote:

Even primes seem abstractly possible.. The Sieve of Archimedes (was it
Archimedes?

Sieve of Eratosthenes.

Eratoshtenes was a very clever man who ran the Library at Alexandria. Among his accomplishments was the measurement of the circumference of the Earth to within 5 percent of its modern value.

He also proposed that a leap day be added every fourth year to keep the seaons in line with the months.

http://scienceworld.wolfram.com/biography/Eratosthenes.html

Bob Kolker