The Sieve of Eratosthenes  

Eratosthenes of Cyrene was one of the great scientists of antiquity. He taught that the earth is a ball and by ingenious application of the methods of elementary geometry (at a time when most people thought that the earth is a flat disk) he determined its circumference with an amazing precision to be equal to 250000 "stadiums". This value corresponds roughly to 46000 kilometres. Today, as a more exact value the circumference of the earth's equator is taken to be 40075 kilometres.  

Furthermore, the name of Eratosthenes is connected with the Sieve of Eratosthenes. This procedure to generate prime numbers is described as follows.  

The Sieve of Eratosthenes (general description):    The-Sieve-of-Eratosthenes-Text 

Here is an interactive simulation (suitable for experiments) of the Sieve of Eratosthenes:  Sieve-of-Eratosthenes-Simulation  

Some remarks on the simulation:  

• The simulation can be started by input of the upper limit and the column number - followed by pressing the "Start" button.
  Alternatively, with empty input fields, it can be started by pressing the Start button - in which case the default values for the upper limit and number of columns will be applied.  After pressing the Start button the initial range of numbers is displayed in an array of rows and columns.     
• By choosing different colors and shapes for representing the process of "crossing out", various patterns appear in the course of the Sieve procedure. These patterns can be varied by using different column numbers.
• Reaching or exceeding the root of the upper limit is signalled visually. This serves the purpose of showing that after reaching the root of the upper limit no new numbers are crossed out.
• After finishing the Sieve procedure all the primes found are printed out.