Prime number

What is a Prime number?

• Prime numbers are whole numbers greater than 1, that have only two factors 1 and the number itself.
• Prime numbers are divisible only by the number 1 or itself.

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Prime number Example

For example, 2, 3, 5, 7, and 11 are the first few prime numbers.

• The factor of 2 is (1,2)
• The factor of 3 is (1,3)
• The factor of 5 is (1,5)
• The factor of 7 is (1,7)

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Prime numbers up to 100

• List of all the prime numbers up to 100, marked in red.

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Prime number – Properties

• p is prime if it has only two factors {1,p}
• 1 is not prime , as it has only one factor 1
• Every number can be decomposed into prime factors

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Example: 12

• • 12 = 2*2*3 = 2² *3 
  • 12 has factors 2 & 3.
  • 2 & 3 are prime numbers

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Example: 126

• • 126 = 2*3*3*7 = 2*3² *7
  • 126 has factors 2 , 3 & 7
  • 2, 3, & 7 are prime numbers

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• This decomposition is unique — it is known as prime factorization

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