Check Prime Number by using PHP

<?php

if(isset($_POST['Check'])) {

$checkNumber = $_POST['number'];

if($checkNumber %2 !== 0 && $checkNumber / $checkNumber == 1 )

{

echo "<h1>" . $checkNumber . "   " . "Prime Number" . "</h1>";

}

elseif($checkNumber % 2 ==0)

{

echo "<h1>" . $checkNumber . "   " . "Not Prime Number" . "</h1>";

}

else{

echo "<h3>" . "Nothing Found ! Please Input Number To Ckeck Prime ?" . "</h3>";

}

}

?>

<form name="myForm" method="post" action="">

Input Number:

<input type="text" name="number" placeholder="Input Number">

<input type="submit" name="Check" value="Check">

</form>