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May 20th

May 20th

# Prime Numbers

A prime number is a number that is divisible by 1 and itself only. Numbers that are notprime are called composite numbers. The smallest prime number is 2. It is also the onlyeven prime number. The prime numbers from 2 to 100 should be memorized. I suggestmemorizing the primes in sets of 10. For example, learn that 53 and 59 are the only primenumbers in the 50s.

List of Prime Numbers

 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

Questions involving prime numbers could ask for one specific prime number greater thanor less than another number, or how many primes are within a specific range.

Example:

What is the greatest prime number less than 25?

Knowing all the primes in the 20s (23, 29), the greatest prime less than 25 is 23.

Example:

How many primes are between 10 and 20?

Knowing all the primes in the 10s (11, 13, 17, 19), there are 4 prime numbers from 10 to 20.

Learning primes is important because many other tricks come from knowing prime numbers,including prime factorization, least common multiple, greatest common divisor, andothers.

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