Prime Numbers and Composite Numbers

Applied Mathematics

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Prime Numbers

Numbers having factors and number itself are known as prime numbers.
As for example, take number .
Factors of are and
Therefore, is a prime number.

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Composite Numbers

Composite numbers are numbers which have at least one factor other than number itself and .
Examples of composite number are   , , .
Factors of are

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Twin Primes

Prime Numbers which differ by are called Twin Primes
Example: ,

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Co- Prime Numbers

If two numbers have their greatest common divisor to be then those numbers are said to be co-prime.
In number theory, two integers and are said to be relatively prime, mutually prime, or coprime (also spelled co-prime) if the only positive integer that evenly divides both of them is . That is, the only common positive factor of the two numbers is . This is equivalent to their greatest common divisor being .

Example: and are co-primes to each other.