Prime number

 History of Prime Numbers

The prime number was discovered by Eratosthenes (275-194 B.C., Greece). He took the example of a sieve to filter out the prime numbers from a list of natural numbers and drain out the composite numbers.


Students can practise this method by writing the positive integers from 1 to 100, circling the prime numbers, and putting a cross mark on composites. This kind of activity refers to the Sieve of Eratosthenes.


Properties of Prime Numbers

Some of the properties of prime numbers are listed below:


Every number greater than 1 can be divided by at least one prime number.

Every even positive integer greater than 2 can be expressed as the sum of two primes.

Except 2, all other prime numbers are odd. In other words, we can say that 2 is the only even prime number.

Two prime numbers are always coprime to each other.

Each composite number can be factored into prime factors and individually all of these are unique in nature.


Prime Numbers Chart

Before calculators and computers, numerical tables were used for recording all of the primes or prime factorizations up to a specified limit and are usually printed. The most beloved method for producing a list of prime numbers is called the sieve of Eratosthenes. This method results in a chart called Eratosthenes chart, as given below. The chart below shows the prime numbers up to 100, represented in coloured boxes.


Prime Numbers

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