Stimulating Understanding of Computational science through Collaboration, Exploration, Experiment, and Discovery for students with Hearing Impairments
a collaboration of the Shodor Education Foundation, Inc., Eastern North Carolina School for the Deaf, Barton College, the National Technical Institute for the Deaf, and Interpreters, Inc.

For Teachers!

Sieve of Eratosthenes

Directions for using the model and finding prime numbers.

First, choose the size of the group of numbers to investigate for primes. The default is 5 rows by 10 columns, or the
numbers from 1 to 50. 

You will notice that the number 1 is a different color because 1 is neither prime nor composite. 

The program starts with the smallest prime number, 2. Since 2 is prime, it changes color. If a number is divisible by 2,
then it is not prime. Therefore, you must cross it off. To do this, click every number divisible by 2. When you correctly
click a number, the number will change color. The model will tell you when you have found them all. Choose
"Auto-Color!" to automatically cross off all of the multiples of 2. 

The program will then move to the next number not crossed off, which is a prime number. This is the number 3. You must
now cross off every number that is divisible by 3. (Remember, if a number is divisible by 3, then it is composite.) 

This pattern continues until only the primes are left. 

Press "Reset" to start the program over. 

Developed by
The Shodor Education Foundation, Inc.

Copyright © 1999-2001 by The Shodor Education Foundation, Inc.

This project is supported, in part, by the National Science Foundation Opinions expressed are those of the authors and not necessarily those of the National Science Foundation.