Simple Factorial Program in PHP

The factorial of a number is the product of all integers up to and including that number, so the factorial of 4 is 4*3*2*1= 24.

<?php
// Formula: n! = n*(n-1)*(n-2)*(n-3)...3.2.1 and zero factorial is defined as one i.e. 0! = 1.

// Method 1. Using for loop
$fact = 1;
$number = 5;

for ($i = 1; $i <= $number; $i++)
    $fact = $fact * $i;

echo $fact;

//----------------------------------
// Method 2: Using recursive method

function factorial($n) {
    if ($n == 0)
        return 1;
    else
        return($n * factorial($n - 1));
}
$number=6;
echo factorial($number);
?>

Simple Prime number program in PHP

Que: What is Prime number?
Ans: A number is prime if it is divisible only by one and itself. (Ex: 2, 3, 5, 7, 11, 13, 17....etc)

Program:

<?php
$num = 4; // <=== Replace desired number to check
for ($i = 2; $i <= $num - 1; $i++) {
    if (bcmod($num, $i) == 0) {
        echo $num . " is not prime number :(";
        break;
    }
}
if ($num == $i)
    echo $num . " is prime number :)";
?>

Fibonacci Series in PHP

Que: What is Fibonacci Series?
Ans: Numbers of Fibonacci sequence are known as Fibonacci numbers. First few numbers of series are 0, 1, 1, 2, 3, 5, 8 etc, Except first two terms in sequence every other term is the sum of two previous terms, For example 8 = 3 + 5 (addition of 3, 5)

Fibonacci Series using for loop:

<?php
$term = 10;
$num1 = 0;
$num2 = 1;

for ($i = 0; $i < $term; $i++) {
    if ($i <= 1)
        $result = $i;
    else {
        $result = $num1 + $num2;
        $num1 = $num2;
        $num2 = $result;
    }
    echo "<br>" . $result;
}
?>

Fibonacci Series using recursion:

<?php

function fibonacci($n) {
    if ($n == 0)
        return 0;
    else if ($n == 1)
        return 1;
    else
        return ( fibonacci($n - 1) + fibonacci($n - 2) );
}

$term = 10;
for ($i = 1; $i <= $term; $i++) {
    echo "<br>".fibonacci($c);
    $c++;
}
?>

Output: 0 1 1 2 3 5 8 13 21 34