Eratosthenes of Cyrene (276 BCE - 194 BCE), a Greek mathematician (among other things), was chief librarian of the Great Library of Alexandria. He also devised a system of latitude and longitude, and was the first known person to have calculated the circumference of the Earth.

He also invented a method of finding Prime Numbers, called the Sieve Of Eratosthenes, that doesn't require division (although most people implement this incorrectly and do use division.)

One of the Famous People on this site.