Solved ProjectEuler/021: php, ruby, c

ProjectEuler/021/solve.php

@@ -0,0 +1,23 @@
+<?php
+define('MAX',10000);
+
+function d($int) {
+	static $cache;
+	if(isset($cache[$int])) {return $cache[$int]; }
+	$sum = 0;
+	for($n=1;$n<$int;$n++) {
+		if($int % $n == 0)
+			$sum += $n;
+	}
+	$cache[$int] = $sum;
+	return $sum;
+}
+
+$result = 0;
+for($number = 1; $number < MAX; $number++) {
+	$d_sum = d($number);
+	if($number != $d_sum AND $number == d($d_sum)) {
+		$result += $number;
+	}
+}
+echo $result;