Eratosthenes lived from 271-194 B.C. He was born in Cyrene which was a Greek colony west of Egypt and under Ptolemaic domination. He spent most of his working days in Alexandria. In his early life, he studied at Plato's school in Athens. He held one of the most prestigous postitions in the Hellenistic world, chief librarian at the Museum. He has written works on geography, philosophy, history, astronomy, mathematics, and literary criticism.

One of Eratosthenes' contributions to mathematics was his measurement of the Earth. He calculated the circumference of the Earth to be about 252,000 stadi which is equal to about 24,662 miles. Eratosthenes is known in number theory for his sieve, the sieve of Eratosthenes, which finds all primes less than a given integer n.

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