I've tried to port the following sum in a php for loop

Bu yol:

    $prod = 1;

for($i=0;$i<$_POST["capacity"];$i++){
$prod = $prod * (($_POST["capacity"] - (i+1)) / $toffered);
} 
    ?>
p(c) is:  <?php echo floatval(1.00/floatval((1+ floatval($prod)))); ?><br /> <br />

ama nedense bana yanlış sonuç verebilir gibi görünüyor. Yanlış ne olduğu hakkında ipuçları?

EDIT: i've modified the initial value of prod as well as adding brackets for i+1 which is subtracted from the capacity. The results aren't better still.