Strong Number Listing and checking if input is strong number or not

Current strong-number check

A strong number equals the sum of the factorials of its digits. Use intdiv() to remove one digit at a time without converting the working value to a float.

<?php
function digitFactorial(int $digit): int
{
    $result = 1;
    for ($i = 2; $i <= $digit; $i++) {
        $result *= $i;
    }
    return $result;
}

$number = 145;
$work = $number;
$sum = 0;

while ($work > 0) {
    $sum += digitFactorial($work % 10);
    $work = intdiv($work, 10);
}

echo $sum === $number ? 'Strong number' : 'Not a strong number';
?>

A number is called strong number if the number is equal to the sum of factorials of digits of the number.

Example :
Number 145 is a strong number as sum of factorial of 1 , 4 and 5 is equal to 145
145= 1! + 4! + 5!

Checking Strong number and generating all strong numbers within a range in PHP

There are three parts in this script.

Function to get Factorial of a number
Collecting all digits of the number
Finding sum of the factorial of digits and comparing

Function to get Factorial of a number

We will use one function to get the factorial of any input number.

function fact($n){
$factorial=1;
for ($i=1; $i<=$n;$i++){
	$factorial=$factorial*$i;
}
return $factorial;
}

Getting all digits of the input number.

$n1=1234; // Sample number  
while($n1>0){
	$d=$n1%10; // reminder of division 
	echo $d; // one digit from right
	$n1=floor($n1/10); // floor value
}

Using the above two concepts we can find out the sum of factorial of any number. We will create one sticky form to take user input and then find out it is strong number or not.

<?Php
$n1=$_POST['n1'] ?? '';
echo "<form method=POST action=''>
<input type=text name=n1 value='$n1'> 
<input type=submit value=Submit>
</form>";
function fact($n){
$factorial=1;
for ($i=1; $i<=$n;$i++){
	$factorial=$factorial*$i;
}
return $factorial;
}
$sum=0;
$n2=$n1;
while($n1>0){
	$d=$n1%10; // reminder of division 
	$sum = $sum  + fact($d);
	$n1=floor($n1/10); // floor value
}
if($n2==$sum){
	
echo "$n2 is  a Strong Number ";	
}else{
echo "$n2 is NOT a Strong Number ";		
}
?>

Listing all strong numbers

Without taking user input we can list all strong number over a range. We can find out all strong numbers less than 100000.

<?Php
function fact($n){
$factorial=1;
for ($i=1; $i<=$n;$i++){
	$factorial=$factorial*$i;
}
return $factorial;
}
for($i=10;$i<100000;$i++){
$sum=0;
$n2=$n1=$i;
while($n1>0){
	$d=$n1%10; // reminder of division 
	$sum = $sum  + fact($d);
	$n1=floor($n1/10); // floor value
}
if($n2==$sum){
echo "$n2 is  a Strong Number <br> ";	
}

}
?>

Output

145 is a Strong Number
40585 is a Strong Number

Introduction to PHP Factorial of a number Sum of Digits of a number
Armstrong number Fibonacci Series
Basic Codes Check the string or number is Palindrome or not in PHP

Subhendu Mohapatra

Author & Instructor at plus2net

I write and maintain practical tutorials on Python, PHP, SQL, JavaScript, HTML, jQuery, and web development at plus2net. The tutorials focus on clear explanations, working examples, and code that readers can test and adapt while learning.

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Checking Strong number in PHP

Current strong-number check

Function to get Factorial of a number

Listing all strong numbers

Subhendu Mohapatra