ORE Number Java

The ORE number is a special positive number which is also known as a harmonic divisor number. A number is said to be ORE if its divisors have a harmonic value as an integer. Unlike Prime and Armstrong numbers, the ORE number is rarely asked by the interviewers.

Let's take some examples of ORE numbers.

6 is an ORE number because its harmonic mean of the divisor, i.e., 2 is an integer.
4 is not an ORE number because its harmonic mean of the divisor is not an integer.
28 is also an ORE number because its harmonic mean of the divisor, i.e., 4 is an integer.

Let's understand how we can calculate the harmonic mean of the number mathematically:

Number=6

Factors of number 6=1,2,3,and 6

Harmonic mean = n / (∑1/x_i)

Here, n is the number of factors, and x is the value of the factor. So,

The harmonic mean of the number 6 is 2, i.e., a positive integer value, so it is an ORE number.

Steps to check ORE number

In order to check whether the number is ORE or not, we have to follow the following steps:

We first take a number from the user to check.
After that, we find all the divisors of that number to find the harmonic mean.
Next, we calculate the harmonic mean of the number using the divisors list.
If the harmonic mean of the number is an integer, we print "number is an ORE number.". Otherwise, print "number is not an ORE number.".

Note: In order to find the harmonic mean of the number, we have to implement our own logic. There is no predefined function to get the harmonic mean of the number.

Let's implement the code to check whether the number is an ORE number or not.

ORENumber.java

//import required classes and packages
import java.util.*; 
import java.io.*; 
import java.util.Scanner;

//create ORENumber class to check whether the given number is an ORE number or not
class ORENumber { 
	
	// create calculateHarmonicMean() method to find the harmonic means of divisors
    static double calculateHarmonicMean(int number)
    {
        Set<Integer> divisors = findDivisors(number);
  
        double sum = 0.0;
  
        for (Iterator<Integer> iterator = divisors.iterator(); iterator.hasNext(); ) {
			Integer data = iterator.next();
			sum = sum + number / data;
		}
		sum = sum / number;
  
        // find the harmonic mean by dividing the size of divisors list with sum and return it
  
        return divisors.size() / sum;
    }
	
	// create findDivisors() method to get all the divisors of the number
    static Set<Integer> findDivisors(int number)
    {
        //create a lsit of integer that will contain divisors of number
		Set<Integer> divisors = new HashSet<Integer>();
		
		// use for loop to get divisors and store them into set 
        for (int i = 1; i <= Math.sqrt(number); i++) {
			//check whether the reminder of the number with i equals to 0 or not 
            if (number % i == 0) {
  
                // add 'i' into divisors list if divisor are equals
                if (number / i == i)
                    divisors.add(i);
  
                else //add 'i' and 'number/i' both if divisors are not equal
                {
                    divisors.add(i);
                    divisors.add(number / i);
                }
            }
        }
		return divisors;
    }
  
    // create checkORENumber() method to check whether the number is ORE or not
    static boolean checkORENumber(int number)
    {
        // find the harmonic mean of the number
        double meanValue = calculateHarmonicMean(number);
  
        // check whether the harmonic mean is an integer or not
        if (meanValue - Math.floor(meanValue) == 0)
            return true;
        else
            return false;
    }
  
    // Driver Code
    public static void main(String[] args)
    {
        int n1, n2;
		
		//create scanner class object to get input from user
		Scanner sc = new Scanner(System.in);
		
		//show custom message
		System.out.println("Enter first number");
		
		//store user entered value into variable n1
		n1 = sc.nextInt();
		
		//show custom message
		System.out.println("Enter second number");
		
		//store user entered value into variable n2
		n2 = sc.nextInt();
		
        if (checkORENumber(n1)) 
            System.out.println(n1 + " is an ORE number"); 
        else
            System.out.println(n1 + " is not an ORE number"); 
        if (checkORENumber(n2)) 
            System.out.println(n2 + " is an ORE number"); 
        else
            System.out.println(n2 + " is not an ORE number");
  
        
    } 
}

Output:

FindAllORENumbers.java

//import required classes and packages
import java.util.*; 
import java.io.*; 
import java.util.Scanner;

//create FindAllORENumbers class to get all the ORE number in the given range
class FindAllORENumbers { 
	
	//main() method start
	public static void main(String args[])
	{
		int range;
		
		//create scanner class object
		Scanner sc=new Scanner(System.in);
		
		//show custom message
		System.out.println("Enter the value of range");
		
		//store user entered value into variable range
		range = sc.nextInt();
		
		System.out.println("The ORE Numbers between 0 and " + range + "are:");
		for(int i = 1; i <= range; i++){
			if(checkORENumber(i))
				System.out.println(i);
		}
	}
	
	// create checkORENumber() method to check whether the number is ORE or not
    static boolean checkORENumber(int number)
    {
        // find the harmonic mean of the number
        double meanValue = calculateHarmonicMean(number);
  
        // check whether the harmonic mean is an integer or not
        if (meanValue - Math.floor(meanValue) == 0)
            return true;
        else
            return false;
    }
	
	// create calculateHarmonicMean() method to find the harmonic means of divisors
    static double calculateHarmonicMean(int number)
    {
        Set<Integer> divisors = findDivisors(number);
  
        double sum = 0.0;
  
        for (Iterator<Integer> iterator = divisors.iterator(); iterator.hasNext(); ) {
			Integer data = iterator.next();
			sum = sum + number / data;
		}
		sum = sum / number;
  
        // find the harmonic mean by dividing the size of divisors list with sum and return it
  
        return divisors.size() / sum;
    }
	
	// create findDivisors() method to get all the divisors of the number
    static Set<Integer> findDivisors(int number)
    {
        //create a lsit of integer that will contain divisors of number
		Set<Integer> divisors = new HashSet<Integer>();
		
		// use for loop to get divisors and store them into set 
        for (int i = 1; i <= Math.sqrt(number); i++) {
			//check whether the reminder of the number with i equals to 0 or not 
            if (number % i == 0) {
  
                // add 'i' into divisors list if divisor are equals
                if (number / i == i)
                    divisors.add(i);
  
                else //add 'i' and 'number/i' both if divisors are not equal
                {
                    divisors.add(i);
                    divisors.add(number / i);
                }
            }
        }
		return divisors;
    }
}

Output: