Prime Numbers

Prime Number is a natural number greater than 1 that has exactly two distinct natural number divisors: 1 and itself. A natural number greater than 1 that is not a prime number is called a composite number.

For example, 13 can only be divided by 1 and by 13 itself.

Here is a list of all the prime numbers up to 100:

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,..

1 is not a prime number as in definition “For a number to be prime it must have two distinct (different) factors.

Algorithm

Step1: Input the number(n) to check for prime number

Step2: If n is below or equal to 1 then go to step 12

Step3: if n is equal to 2 then go to step 11

Step4: Assign variable count =n / 2

Step5: Assign variable a=1

Step6: Add 1 to a and store it to variable a

Step7: remainder = n % a

Step8: if remainder=0 then go to step 12

Step9: subtract one from count and store it to variable count

Step10: if count is not equal to 0 then go to step 6

Step11: Display “it is a prime number”: go to step 13

Step12: Display “it is not a prime number”

Step13: Stop

In the first step we will read the number(n) inputted by user to check for prime number.

In the next step, we will check if the number(n) is below or equal to 1 if its true then that number cannot be a prime number

In third step, we will check if number(n) is equal to 2 if its true then it is prime number.

As now the number is greater than 2 , we will find if number(n) is divisible by any other number than itself and 1. If its divisible by any number then its not a prime number otherwise it’s a prime number.

We will use the modulus operator to find out the remainder and check if remainder is 0 or not, if the remainder is 0 then its not a prime number.

The modulus, or remainder, operator divides number1 by number2 and returns only the remainder. The sign of the result is the same as the sign of number1. The modulus operator is represented as mod or %