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- <?php
- function isprime ($num) {
- $i = (int)(sqrt($num));
- while ($i>1) {
- if ($num%$i==0) {
- return 0;
- }
- $i--;
- }
- return 1;
- }
- $input = 600851475143;
- $largest = 0;
- $j = (int)(sqrt($input)+1);
- while($j>1) {
- if (intval(fmod($input,$j))==0) {
- if (isprime($j)) {
- $largest = $j;
- break;
- }
- }
- $j--;
- }
- echo $largest;
- ?>
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