Something

<?php

$a = array();
for ($i = 0; $i < 1000; $i++)
	$a[$i] = true;

for ($i = 2; $i <= 1000; $i++)
	for ($j = 0; $j < 1000; $j += $i)
		$a[$j] = !$a[$j];

$open = array();
$c = 0;
for ($i = 0; $i < 1000; $i++) {
	if ($a[$i]) {
		$open[] = $i;
		$c++;
	}
}

echo $c . ": " . implode(', ', $open) . "\n";

?>