Learn to test whether a given number is prime number or not

By looking at a number do you wonder whether it’s a prime number or not?
Is it always complicated for you to figure out the answer?

If the answer to above questions is yes, go ahead and learn this method of figuring out if a number is prime or not.

To test whether any number is a prime number or not, take an integer larger than the approximate square root of that number.

To quickly find the square root of any number, you can look at finding square root without calculator and Heron’s Method of finding roots.

Let say the square root of the said number is ‘x’. Test the divisibility of the given number by every prime number less than ‘x’. If it is not divisible by any of them then it is prime number; otherwise it is a composite number (other than prime).

Example 1: Is 349 a prime number?
The square root of 349 is approximately 19. The prime numbers less than 19 are 2, 3, 5, 7, 11, 13, 17.
Clearly, 349 is not divisible by any of them. Therefore, 349 is a prime number.

Example 2: Is 881 a prime number?
The square root of 881 is approximately 30. The prime numbers less than 30 are 2, 3, 5, 7, 11, 13, 17, 19, 23, 29.
881 is not divisible by any of the above numbers. Therefore, 881 is a prime number.

If you know other ways of finding if a number is prime number or not, share it with all by posting a comment below.

2 Comments
  1. nikhil

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