## -0276 – Eratosthenes – bio

Eratosthenes was born in -0276 in Cyrene, then a Greek colony, now part of Lebanon and was a mathematician and astronomer and is considered the father of the field known today as geography. He studied in Athens and Alexandria and was a librarian of the great library at Alexandria. He was the first to use the word, “geography”, made some of the most accurate geographical measurements of the time and created a system of latitude and longtitude to aid with such measurements.

Prime numbers are numbers that cannot be divided by any number other than itself and one. The sieve of Eratosthenes is a method of finding prime numbers by eliminating all numbers that are products of numbers previously considered. Start with two and eliminate all numbers that are multiples of two. Then consider three and eliminate all numbers that are multiples of three. Then consider five (four has already been eliminated) and eliminate all numbers that are multiples of five. Six, eight, nine, ten, twelve, fourteen, fifteen, sixteen, eighteen and twenty have now been eliminated. Still remaining are 2, 3, 5, 7, 11, 13, 17, 19 which are prime numbers. Prime numbers are particulary useful in crypotography.

PRECURSOR:
-0575 – Pythagoras
-0460 – Zeno
Aristotle
-0325 Euclid

CONCURRENT:
-0287 – Archimedes

SUBSEQUENT:
Nichomachus
0085 – Ptolemy
1588 – Mersenne
1601 – Fermat
1690 – Goldbach
1707 – Euler
1752 – Legendre
1777 – Gauss
1826 – Riemann
1928 – Nash