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Count of square free divisors of a given number
  • Last Updated : 23 Apr, 2021

Given an integer N, the task is to count the number of square-free divisors of the given number. 

A number is said to be square-free, if no prime factor divides it more than once, i.e., the largest power of a prime factor that divides N is one.

 Examples: 

Input: N = 72 
Output:
Explanation: 2, 3, 6 are the three possible square free numbers that divide 72.

Input: N = 62290800 
Output: 31 
 



Naive Approach: 
For every integer N, find its factors and check if it is a square-free number or not. If it is a square-free number then increase the count or proceed to the next number otherwise. Finally, print the count which gives us the required number of square-free divisors of N
Time complexity: O(N3/2)

Efficient Approach: 
Follow the steps below to solve the problem:  

  • From the definition of square-free numbers, it can be understood that by finding out all the prime factors of the given number N, all the possible square-free numbers that can divide N can be found out.
  • Let the number of prime factors of N be X. Therefore, 2X – 1 square-free numbers can be formed using these X prime factors.
  • Since each of these X prime factors is a factor of N, therefore any product combination of these X prime factors is also a factor of N and thus there will be 2X – 1 square free divisors of N.

Illustration: 

  • N = 72
  • Prime factors of N are 2, 3.
  • Hence, the three possible square free numbers generated from these two primes are 2, 3 and 6.
  • Hence, the total square-free divisors of 72 are 3( = 22 – 1).

Below is the implementation of the above approach: 

C++




// C++ Program to find the square
// free divisors of a given number
#include <bits/stdc++.h>
using namespace std;
 
// The function to check
// if a number is prime or not
bool IsPrime(int i)
{
    // If the number is even
    // then its not prime
    if (i % 2 == 0 && i != 2)
        return false;
 
    else {
        for (int j = 3;
             j <= sqrt(i); j += 2) {
            if (i % j == 0)
                return false;
        }
        return true;
    }
}
 
// Driver Code
int main()
{
    // Stores the count of
    // distinct prime factors
    int c = 0;
    int N = 72;
 
    for (int i = 2;
         i <= sqrt(N); i++) {
 
        if (IsPrime(i)) {
            if (N % i == 0) {
                c++;
                if (IsPrime(N / i)
                    && i != (N / i)) {
                    c++;
                }
            }
        }
    }
 
    // Print the number of
    // square-free divisors
    cout << pow(2, c) - 1
         << endl;
    return 0;
}

Java




// Java program to find the square
// free divisors of a given number
import java.util.*;
 
class GFG{
     
// The function to check
// if a number is prime or not
static boolean IsPrime(int i)
{
     
    // If the number is even
    // then its not prime
    if (i % 2 == 0 && i != 2)
        return false;
    else
    {
        for(int j = 3;
                j <= Math.sqrt(i);
                j += 2)
        {
           if (i % j == 0)
               return false;
        }
        return true;
    }
}
 
// Driver code
public static void main(String[] args)
{
     
    // Stores the count of
    // distinct prime factors
    int c = 0;
    int N = 72;
     
    for(int i = 2;
            i <= Math.sqrt(N); i++)
    {
       if (IsPrime(i))
       {
           if (N % i == 0)
           {
               c++;
               if (IsPrime(N / i) &&
                     i != (N / i))
                   c++;
           }
       }
    }
     
    // Print the number of
    // square-free divisors
    System.out.print(Math.pow(2, c) - 1);
}
}
 
// This code is contributed by sanjoy_62

Python3




# Python3 program to find the square
# free divisors of a given number
import math
 
# The function to check
# if a number is prime or not
def IsPrime(i):
     
    # If the number is even
    # then its not prime
    if (i % 2 == 0 and i != 2):
        return 0;
         
    else:
        for j in range(3, int(math.sqrt(i) + 1), 2):
            if (i % j == 0):
                return 0;
                 
        return 1;
 
# Driver code
 
# Stores the count of
# distinct prime factors
c = 0;
N = 72;
 
for i in range(2, int(math.sqrt(N)) + 1):
    if (IsPrime(i)):
        if (N % i == 0):
            c = c + 1
 
            if (IsPrime(N / i) and
                 i != (N / i)):
                c = c + 1
                 
# Print the number of
# square-free divisors    
print (pow(2, c) - 1)
 
# This code is contributed by sanjoy_62

C#




// C# program to find the square
// free divisors of a given number
using System;
class GFG{
     
// The function to check
// if a number is prime or not
static Boolean IsPrime(int i)
{
     
    // If the number is even
    // then its not prime
    if (i % 2 == 0 && i != 2)
        return false;
    else
    {
        for(int j = 3;
                j <= Math.Sqrt(i);
                j += 2)
        {
        if (i % j == 0)
            return false;
        }
        return true;
    }
}
 
// Driver code
public static void Main(String[] args)
{
     
    // Stores the count of
    // distinct prime factors
    int c = 0;
    int N = 72;
     
    for(int i = 2;
            i <= Math.Sqrt(N); i++)
    {
        if (IsPrime(i))
        {
            if (N % i == 0)
            {
                c++;
                if (IsPrime(N / i) &&
                        i != (N / i))
                    c++;
            }
        }
    }
     
    // Print the number of
    // square-free divisors
    Console.Write(Math.Pow(2, c) - 1);
}
}
 
// This code is contributed by shivanisinghss2110

Javascript




<script>
 
// Javascript program to find the square
// free divisors of a given number
 
// The function to check
// if a number is prime or not
function IsPrime(i)
{
     
    // If the number is even
    // then its not prime
    if (i % 2 == 0 && i != 2)
        return false;
    else
    {
        for(j = 3; j <= Math.sqrt(i); j += 2)
        {
            if (i % j == 0)
                return false;
        }
        return true;
    }
}
 
// Driver code
 
// Stores the count of
// distinct prime factors
var c = 0;
var N = 72;
 
for(i = 2; i <= Math.sqrt(N); i++)
{
    if (IsPrime(i))
    {
        if (N % i == 0)
        {
            c++;
             
            if (IsPrime(N / i) &&
                  i != (N / i))
                c++;
        }
    }
}
 
// Print the number of
// square-free divisors
document.write(Math.pow(2, c) - 1);
 
// This code is contributed by aashish1995
 
</script>
Output: 
3

 

Time Complexity: O(N) 
Auxiliary Space: O(1)
 

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