Factorial

<?php
// https://blog.ruangguru.com/aturan-perkalian-dan-faktorial-dalam-teori-peluang

function factorial($n) {
    echo "$n! = ";
    $f = 1;
    for($i=1; $i<=$n; $i++) {
        $f = $f * $i;
        echo "$i" . ( ($i<$n)? "." : "" );
    }

    echo "= $f <br/>";
}

// Test

//2! = 2.1 = 2
factorial(2);
//3! = 3.2.1 = 6
factorial(3);
//4! = 4.3.2.1 = 24
factorial(4);
//5! = 5.4.3.2.1 = 120
factorial(5);

?>