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:

PHP Prime number 1


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.

 

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