togli il while.... e conta solo con il for

codice:
<?php
echo "<FORM NAME=\"tabella\" method=\"post\" action=".$_SERVER['PHP_SELF'].">";

   for ($y=1; $y<=16; $y++ )  {
        $temp="lett$y";
        $valore=$$temp;
        echo "<td size='40%'><center>".$valore."</center>";
		if($y%4 == 0)echo  "<tr>";
    }