Program to Check if Two Numbers are a Friendly Pair in C++

Friendly Pair

A friendly pair (also called an amicable pair) is a pair of numbers where the sum of their proper divisors divided by the number itself results in the same value for both numbers. For example, (220, 284) is a friendly pair.

We will explore a method to check if a given pair of numbers is a friendly pair using C++ programming.

Method: Using a Function

We calculate the sum of proper divisors for both numbers and check if their ratios match.

#include <iostream>
using namespace std;

int sumOfDivisors(int num) {
    int sum = 0;
    for (int i = 1; i <= num / 2; i++) {
        if (num % i == 0) {
            sum += i;
        }
    }
    return sum;
}

int main() {
    int num1, num2;
    cout << "Enter two numbers: ";
    cin >> num1 >> num2;
    
    int sum1 = sumOfDivisors(num1);
    int sum2 = sumOfDivisors(num2);
    
    if ((double)sum1 / num1 == (double)sum2 / num2)
        cout << num1 << " and " << num2 << " are a Friendly Pair";
    else
        cout << num1 << " and " << num2 << " are not a Friendly Pair";
    
    return 0;
}
            

Output:

Enter two numbers: 220 284
220 and 284 are a Friendly Pair