PrimeNumber

<?php
$submit=$_POST['submit'];
$prime=$_POST['n'];

//if($n===1){
//    echo"not a prime or composite no";
//}

if($prime==1){
    echo"not a prime or composite no";
}
for($index=2;$index<=$prime/2;$index++){
   
    if($prime%$index===0){
        $set=1;
    }
 
}
if($set){
    echo $prime." is a composite number";
}else{
    echo $prime." is a prime number";
}


?>

<form action="#" method="post" enctype="multipart/form-data">
   
    <table>
        <tr>
            <td><input type="text" name="n"></td>
            <td><input type="submit" name="submit" value="submit"></td>
        </tr>
    </table>
   
</form>