Nota

<!DOCTYPE html>
<html>
<head>
    <title>Nota</title>
    <style type="text/css">
    .box {border:1px solid #444;padding:10px;text-align:center;max-width:300px;}
    </style>
</head>
<body>
<div class="box">
<?php
$nourut = @$_POST['nilai'];
$nourut++;
?>
    <form method="POST">
        <button type="submit" name="submit">GENERATE</button>
        <input type="hidden" name="nilai" value="<?php echo $nourut ?>">
    </form>
    <?php
    if(isset($_POST['submit'])) {
        echo 'N'.date('dmy').'-'.sprintf('%04s', $nourut-1);
    }
    ?>
</div>
</body>
</html>