# Prime Number

A number which is only divisible by 1 and itself is called prime number. Numbers 2, 3, 5, 7, 11, 13, 17, etc. are prime numbers.

• 2 is the only even prime number.
• It is a natural number greater than 1 and so 0 and 1 are not prime numbers.

## Prime number in PHP

Example:

Here is the Program to list the first 15 prime numbers.

1. <?php
2. \$count = 0;
3. \$num = 2;
4. while (\$count < 15 )
5. {
6. \$div_count=0;
7. for ( \$i=1; \$i<=\$num\$i++)
8. {
9. if ((\$num%\$i)==0)
10. {
11. \$div_count++;
12. }
13. }
14. if (\$div_count<3)
15. {
16. echo \$num.” , “;
17. \$count=\$count+1;
18. }
19. \$num=\$num+1;
20. }
21. ?>

Output: ## Prime Number using Form in PHP

Example:

We’ll show a form, which will check whether a number is prime or not.

1. <form method=“post”>
2. Enter a Number: <input type=“text” name=“input”><br><br>
3. <input type=“submit” name=“submit” value=“Submit”>
4. </form>
5. <?php
6. if(\$_POST)
7. {
8.     \$input=\$_POST[‘input’];
9.     for (\$i = 2; \$i <= \$input-1; \$i++) {
10.       if (\$input % \$i == 0) {
11.       \$value= True;
12.       }
13. }
14. if (isset(\$value) && \$value) {
15.      echo ‘The Number ‘\$input . ‘ is not prime’;
16. }  else {
17.    echo ‘The Number ‘\$input . ‘ is prime’;
18.    }
19. }
20. ?>

Output:

On entering number 12, we get the following output. It states that 12 is not a prime number. On entering number 97, we get the following output. It states that 97 is a prime number.