This site is completly written in PHP5
It's also a valid HTML5 and CSS
Under Construction

<?php
    echo amIprime($num);
    
    function amIprime($num,$i=1){
        return (is_numeric($num)) 
            ? (($num<=20020) 
                ? (($num%$i==0 && $i!=1 && $num!=2) 
                    ? "Not Prime Number" 
                    : (($i<=$num/2) 
                        ? amIprime($num,++$i) 
                        : "Prime Number")) 
            : "This isn't a number";
    }  
?>
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