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Title : Prime number finder (Sieve of Erastothenes)
Categories : PHP, Algorithms, Math. Click here to Update Your Picture
Chao Xu
Date : May 15th 2007
Grade : 3 of 5 (graded 2 times)
Viewed : 2153
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This script uses Sieve of Erastothenes to find all the prime up to a number

<?php
//Made by Chao Xu
//http://webdevlogs.com/
function esprime($limit){
       
$sqrtlimit = sqrt($limit);
$range = 0;
while(
$range<$limit){
       
$i .= '11';
       
$range+=2;
}
       
$n = 2;
        while(
$n < $sqrtlimit){
                if (
$i[$n]){
                       
$sqn = $n*$n;
                       
$k = $sqn;
                       
$i[$k]=0;
                        while(
$k<=$limit){
                               
$k += $n;
                               
$i[$k]=0;
                        }
                }
                ++
$n;
        }
       
$n = 1;
        while(
$n<$limit){
                if(
$i[$n]) $primes[] = $n;
               
$n+=2;
        }
        if(
$limit>=2) $primes[0] = 2;
        return
$primes;
}
?>



It returns an array of all prime number below an the argument.
<?php
esprime
(6);
//return array(2,3,5);
?>



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