Maharashtra State BoardSSC (English Medium) 5th Standard

Concept of Sieve of Eratosthenes




Eratosthenes chart of prime numbers:

Greek Mathematician Eratosthenes, in the third century B.C., Let us see the method. List all numbers from 1 to 100, as shown below.

Step 1: Cross out 1 because it is not a prime number.

Step 2: Encircle 2, cross out all the multiples of 2, other than 2 itself, i.e. 4, 6, 8, and so on.

Step 3: You will find that the next uncrossed number is 3. Encircle 3 and cross out all the multiples of 3, other than 3 itself.

Step 4: The next uncrossed number is 5. Encircle 5 and cross out all the multiples of 5 other than 5 itself.

Step 5: Continue this process till all the numbers in the list are either encircled or crossed out. All the encircled numbers are prime numbers. All the crossed-out numbers, other than 1 are composite numbers. This method is called the Sieve of Eratosthenes.

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