Enter Number to stop at

Using the Sieve of Eratosthenes

How many prime numbers < 40

Using the Sieve of Eratosthenes

Remove all multiples of 2

Remove all multiples of 3

Remove all multiples of 5

List all numbers from 2 to 40
2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40
2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40
2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40
2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40

Since the next prime number is 7
72 = 49 > 40, we stop here

Stopping Point

We have 12 prime numbers < 40

2,3,5,7,11,13,17,19,23,29,31,37

Final Answer


This is also written as π(40) = 12

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