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Prime Numbers


This topic will be easier for you if you know your fast multiplication.
To review Fast Multipication, see here.

A prime number is a positive number that has only two factors, 1 and itself.

For example, the only factors of 5 are 1 and 5, so 5 is a prime number.
The factors of 6 are 1, 2, 3, and 6 so 6 is not a prime number.

To figure out if a number is a prime number, check to see if the number is divisible by any number besides 1 and itself.

NOTE: 1 is not a prime number.


Examples:

a. 4
  The factors of 4 are 1, 2, and 4.
So 4 is not a prime number.
b. 13
  The factors of 13 are 1 and 13.
So 13 is a prime number.
c. 21
  The factors of 21 are 1, 3, 7, and 21.
So 21 is not a prime number.


Here is a list of the prime numbers under 100.
2 3 5 7 11
13 17 19 23 29
31 37 41 43 47
53 59 61 67 71
73 79 83 89 97

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