<?php
function is_prime($number)
{
foreach (range(2, $number - 1) as $value) {
$remainder = $number % $value;
if ($remainder == 0) {
return false;
}
}
return true;
}
function largest_prime($number)
{
$largest_prime_factor = 0;
foreach (range(2, $number - 1) as $value) {
if (is_prime($value) && $number % $value == 0 && $value > $largest_prime_factor) {
$largest_prime_factor = $value;
}
}
return $largest_prime_factor;
}
print_r(largest_prime(26));
<?php
/**
* Project Euler: Problem 3
* Title: Largest prime factor
* Description: The prime factors of 13195 are 5, 7, 13 and 29.
* What is the largest prime factor of the number 600851475143?
* Author: Jonathan Herbst
* Last Edited: 11/11/2015
*/
function largest_prime($number)
{
$index = 3;
while ($index * $index < $number) {
// If it's a factor
if ($number % $index === 0) {
$number = $number / $index;
} else {
// Iterate by 2 since the answer can't be even
$index += 2;
}
}
// The number that is left over will be the largest prime
return $number;
}
$original = 600851475143;
echo "The largest prime factor of the number " . $original . " is " . largest_prime($original);
