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**C program example for prime number:**

**What is prime number?**

A number is considered as prime number when it satisfies the below conditions.

- It should be whole number
- It should be greated than 1
- It should have only 2 factors. They are, 1 and the number itself.

**Example for prime numbers:** 2, 3, 5, 7, 11, 13, 17, 19, 23 etc.

**Why 4, 6, 8, 9, 10, 12, 14, 15, 16 etc are not prime numbers?**

Because, the number 4 can be factored as 2*2 and 1*4. As per the rule of prime number, there should be 2 factors only. They are 1 and the number itself. But, number 4 has 2*2 also. Like this, all remaining numbers 6, 8, 9, 10, 12, 14, 15, 16 have factors other than 1 and the number itself. So, these are not called as prime numbers.

**Example C program for prime number:**

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#include <stdio.h> int main() { int i, num, p = 0; printf("Please enter a number: \n"); scanf("%d", &num); for(i=1; i<=num; i++) { if(num%i==0) { p++; } } if(p==2) { printf("Entered number is %d "\ "and it is a prime number.",num); } else { printf("Entered number is %d "\ "and it is not a prime number.",num); } } |

**Output of ****C program for prime number:**

Please enter a number: 13
Entered number is 13 and it is a prime number. |