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Prime and Composite Numbers

Sieve of Eratosthenes. Follow these steps:

Step 1: Starting from the first number select the numbers divisible by 2 and choose "div by 2" in the drop box.

Step 2: Among the remaining numbers select the numbers divisible by 3 and choose "div by 3" in the drop box.

Step 3: Continue for numbers divisible by 5 and 7. Remember to work only on the remaining unselected numbers each time.

Step 4: The numbers that finally remain unselected (left behind) are the prime numbers of the group.

Write them in order, in the text boxes below.

15

16

 

17 

18

19

20

21

22

23

24

The prime numbers between 15 and 25 ⇒    ,  and  

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