A Prime Number list generation PHP script


A prime number is defined as a number which can be only divisible by 1 and that number itself. That number cannot be divisible by any other number. So if we try to divide that number by any other number between one and that number , we will get a remainder. According to the prime number definition number one ( 1 ) wont consider as a primer number. The smallest primer number is 2 .

See is a list of primer number below 50
2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47,

Here is a sample PHP script program to create a list of prime numbers
In this example we are going to print first 20 prime numbers.

<?php
$count = 0 ;
$number = 2 ;
while ($count < 20 )
{
$div_count=0;
for ( $i=1;$i<=$number;$i++)
{
if (($number%$i)==0)
{
$div_count++;
}
}
if ($div_count<3)
{
echo $number." , ";
$count=$count+1;
}
$number=$number+1;
}
?>

Its output will be :

2 , 3 , 5 , 7 , 11 , 13 , 17 , 19 , 23 , 29 , 31 , 37 , 41 , 43 , 47 , 53 , 59 , 61 , 67 , 71 ,

Logic of this program : We need first store the current number to a variable. And then we will find the remainder for each division of other numbers with the stored number using a loop. And we will increment a counter if remainder found zero. After all the division operations with other numbers we will check the total counter for the remainder. If its value greater than two means , that number can be divisible by some other number instead of 1 and that number itself.If its value less than three means , its a primer number.

Now look at another PHP script for generating a list of prime numbers below 100.

<?php
$number = 2 ;
while ($number < 100 )
{
$div_count=0;
for ( $i=1;$i<=$number;$i++)
{
if (($number%$i)==0)
{
$div_count++;
}
}
if ($div_count<3)
{
echo $number." , ";
}
$number=$number+1;
}
?>

Its output will be ;

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 ,

This not only the one method of logic to create Primer number series .. You can create the list other methods and loops in PHP.