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Find all factorial numbers less than or equal to n
  • Difficulty Level : Easy
  • Last Updated : 15 Mar, 2021

A number N is called a factorial number if it is the factorial of a positive integer. For example, the first few factorial numbers are
1, 2, 6, 24, 120, …
Given a number n, print all factorial numbers smaller than or equal to n. 
Examples : 
 

Input : n = 100
Output : 1 2 6 24

Input : n = 1500
Output : 1 2 6 24 120 720

 

A simple solution is to generate all factorials one by one until the generated factorial is greater than n.
An efficient solution is to find next factorial using previous factorial. 
 

C++




// CPP program to find all factorial numbers
// smaller than or equal to n.
#include <iostream>
using namespace std;
 
void printFactorialNums(int n)
{
    int fact = 1;
    int x = 2;
    while (fact <= n) {
        cout << fact << " ";
 
        // Compute next factorial
        // using previous
        fact = fact * x;
 
        x++;
    }
}
 
// Driver code
int main()
{
    int n = 100;
    printFactorialNums(n);
    return 0;
}

Java




// Java program to find all factorial numbers
// smaller than or equal to n.
 
class GFG
{
    static void printFactorialNums(int n)
    {
        int fact = 1;
        int x = 2;
        while (fact <= n)
        {
            System.out.print(fact + " ");
     
            // Compute next factorial
            // using previous
            fact = fact * x;
     
            x++;
        }
    }
     
    // Driver code
    public static void main (String[] args)
    {
        int n = 100;
        printFactorialNums(n);
    }
}
 
// This code is contributed by Anant Agarwal.

Python3




# Python3 program to find all factorial
# numbers smaller than or equal to n.
 
def printFactorialNums( n):
    fact = 1
    x = 2
    while fact <= n:
        print(fact, end = " ")
         
        # Compute next factorial
        # using previous
        fact = fact * x
         
        x += 1
 
# Driver code
n = 100
printFactorialNums(n)
 
# This code is contributed by "Abhishek Sharma 44"

C#




// C# program to find all factorial numbers
// smaller than or equal to n.
using System;
 
class GFG
{
    static void printFactorialNums(int n)
    {
        int fact = 1;
        int x = 2;
        while (fact <= n)
        {
            Console.Write(fact + " ");
     
            // Compute next factorial
            // using previous
            fact = fact * x;
     
            x++;
        }
    }
     
    // Driver code
    public static void Main ()
    {
        int n = 100;
        printFactorialNums(n);
    }
}
 
// This code is contributed by vt_m.

PHP




<?php
// PHP program to find all
// factorial numbers smaller
// than or equal to n.
 
function printFactorialNums($n)
{
    $fact = 1;
    $x = 2;
    while ($fact <= $n)
    {
        echo $fact, " ";
 
        // Compute next factorial
        // using previous
        $fact = $fact * $x;
        $x++;
    }
}
 
    // Driver code
    $n = 100;
    echo printFactorialNums($n);
 
// This code is contributed by ajit.
?>

Javascript




<script>
 
// Javascript program to find all factorial numbers
// smaller than or equal to n.
 
function printFactorialNums(n)
{
    let fact = 1;
    let x = 2;
    while (fact <= n) {
        document.write(fact + " ");
 
        // Compute next factorial
        // using previous
        fact = fact * x;
 
        x++;
    }
}
 
// Driver code
 
    let n = 100;
    printFactorialNums(n);
 
// This code is contributed by Mayank Tyagi
     
</script>

Output: 
 

1 2 6 24

Time Complexity : O(n)
If there are multiple queries, then we can cache all previously computed factorial numbers to avoid re-computations.
This article is contributed by Shubham Sagar. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.
Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.
 

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