Un 'altra strada:

codice:
 $buffer = " 1  2  3  4  5  6  7  8  9  10 ";
        $new='';

while($row = mysql_fetch_row($res))
           {

            foreach($row as $value)
                    {
                    $new = " $value ";
                    $buffer = str_replace($new,'',$buffer);
                    }
           }
           echo "I numeri mancanti sono: $buffer";