Over 2100 years ago,Eratosthenes a Greek astronomer and mathematician,discovered a way to find prime number. His method is called the Sieve of Eratosthenes.It is used here to find all the primes in the first 50 whole numbers.
To use the sieve,start by making a list of the whole numbers from 0 to 49. Then follow these steps.
1. Cross out 0 and 1 since they are not prime.
2. The number 2 is pirme. Circle it. Now cross out all multiples of 2. the next number on the list that is not crossed out will be prime. This number is 3. After steps 1 and 2 the sieve looks like this .
Here are the next stepe.
3. Circle 3 and cross out all the multiples of 3. (Some multiples of 3, like 6,12,and18,will already be crossed out.)
4. Circle the next number that is not crossed out. Cross out its multiples.
5.Repeat step 4 until every number in the list is either circled or crossed out.
After all the steps are completed, the sieve looks like this.
Al lthe circled number are prime. What do we call the number, other then 0 or 1, that are crossed out?