Betrothed numbers

Betrothed numbers are two positive numbers such that the sum of the proper divisors of either number is one more than (or one plus) the value of the other number. Our task is to find these pairs efficiently.
Example :

(48, 75) is an example of Betrothed numbers
Divisors of 48 : 1, 2, 3, 4, 6, 8, 12, 
                 16, 24. Their sum is 76.
Divisors of 75 : 1, 3, 5, 15, 25. Their 
                 sum is 49.

Given a positive integer n, print all Brothered numbers (which is a pair) such that one of the numbers in every pair is smaller than n.
Example :

Input : n = 1000
Output : (48, 75)

Input : n = 10000
Output : (48, 75), (140, 195), (1050, 1925)
         (1575, 1648), (2024, 2295), (5775, 
         6128) (8892, 16587), (9504, 20735)



The idea used in below program is simple. We traverse through all numbers from 1 to n-1. For every number num1, we find sum of its proper divisors say sum1. After finding sum1, we check if the number num2 = sum1 + 1 which has sum of divisors as num1 + 1

C++

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// CPP program to find Betrothed number pairs
// such that one of the numbers is smaller than
// a given number n.
#include <iostream>
using namespace std;
  
void BetrothedNumbers(int n)
{
    for (int num1 = 1; num1 < n; num1++) {
  
        // Calculate sum of num1's divisors
        int sum1 = 1; // 1 is always a divisor
  
        // i=2 because we don't want to include
        // 1 as a divisor. 
        for (int i = 2; i * i <= num1; i++) 
        {
            if (num1 % i == 0) {
                sum1 += i;
  
                // we do not want to include 
                // a divisor twice
                if (i * i != num1)
                    sum1 += num1 / i;
            }
        }
  
        // Now check if num2 is the sum of
        // divisors of num1, so only the num 
        // that equals to sum of divisors of 
        // num1 is a nominee for num1.
  
         /* This if is for not to make a 
            duplication of the nums, because 
            if sum1 is smaller than num1, this 
            means that we have already checked 
            the smaller one.*/
        if (sum1 > num1)
        {
            int num2 = sum1 - 1;
            int sum2 = 1;
            for (int j = 2; j * j <= num2; j++) 
            {
                if (num2 % j == 0) {
                    sum2 += j;
                    if (j * j != num2)
                        sum2 += num2 / j;
                }
            }
       
            // checks if the sum divisors of 
            // num2 is equal to num1.
            if (sum2 == num1+1) 
                printf("(%d, %d)\n", num1, num2);
        }
    }
}
  
// Driver code
int main()
{
    int n = 10000; 
    BetrothedNumbers(n);
    return 0;
}

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Java

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// JAVA program to find Betrothed number
// pairs such that one of the numbers is
// smaller than a given number n.
import java.io.*;
  
class GFG{
  
    static void BetrothedNumbers(int n)
    {
    for (int num1 = 1; num1 < n; num1++) {
  
        // Calculate sum of num1's divisors
        int sum1 = 1; // 1 is always a divisor
  
        // i=2 because we don't want to include
        // 1 as a divisor. 
        for (int i = 2; i * i <= num1; i++) 
        {
            if (num1 % i == 0) {
                sum1 += i;
  
            // we do not want to include 
            // a divisor twice
                if (i * i != num1)
                    sum1 += num1 / i;
            }
        }
  
        // Now check if num2 is the sum of
        // divisors of num1, so only the num 
        // that equals to sum of divisors of 
        // num1 is a nominee for num1.
  
        /* This if is for not to make a 
        duplication of the nums, because 
        if sum1 is smaller than num1, this 
        means that we have already checked 
        the smaller one.*/
        if (sum1 > num1)
        {
            int num2 = sum1 - 1;
            int sum2 = 1;
            for (int j = 2; j * j <= num2; j++) 
            {
                if (num2 % j == 0) {
                    sum2 += j;
                    if (j * j != num2)
                        sum2 += num2 / j;
                }
            }
  
        // checks if the sum divisors of 
        // num2 is equal to num1.
            if (sum2 == num1+1
                System.out.println("(" + num1 +
                              ", " + num2 + ")");
        }
    }
    }
  
    // Driver code
    public static void main(String args[])
    {
    int n = 10000
    BetrothedNumbers(n);
    }
}
  
// This code is contributed by Nikita Tiwari.

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Python

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# Python program to find Betrothed number pairs
# such that one of the numbers is smaller than
# a given number n.
  
def BetrothedNumbers(n) :
      
    for num1 in range (1,n) :
          
        # Calculate sum of num1's divisors
        sum1 = 1 # 1 is always a divisor
  
        # i=2 because we don't want to include
        # 1 as a divisor. 
        i = 2
        while i * i <= num1 :
            if (num1 % i == 0) :
                sum1 = sum1 + i
  
                # we do not want to include 
                # a divisor twice
                if (i * i != num1) :
                    sum1 += num1 / i
            i =i + 1
              
        # Now check if num2 is the sum of
        # divisors of num1, so only the num 
        # that equals to sum of divisors of 
        # num1 is a nominee for num1.
  
        # This if is for not to make a 
        #duplication of the nums, because 
        #if sum1 is smaller than num1, this 
        #means that we have already checked 
        #the smaller one.
        if (sum1 > num1) :
              
            num2 = sum1 - 1
            sum2 = 1
            j = 2
            while j * j <= num2 :
                if (num2 % j == 0) :
                    sum2 += j
                    if (j * j != num2) :
                        sum2 += num2 / j
                j = j + 1
                  
            # checks if the sum divisors of 
            # num2 is equal to num1.
            if (sum2 == num1+1) :
                print ('('+str(num1)+', '+str(num2)+')')
                  
# Driver code
  
n = 10000
BetrothedNumbers(n)
  
# This code is contributed by Nikita Tiwari.

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C#

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// C# program to find Betrothed 
// number pairs such that one 
// of the numbers is smaller 
// than a given number n.
using System;
  
class GFG
{
    static void BetrothedNumbers(int n)
    {
    for (int num1 = 1; num1 < n; num1++) 
    {
  
        // Calculate sum of 
        // num1's divisors
          
        // 1 is always a divisor
        int sum1 = 1; 
  
        // i=2 because we don't want 
        // to include 1 as a divisor. 
        for (int i = 2; i * i <= num1; i++) 
        {
            if (num1 % i == 0) 
            {
                sum1 += i;
  
            // we do not want to include 
            // a divisor twice
                if (i * i != num1)
                    sum1 += num1 / i;
            }
        }
  
        // Now check if num2 is the 
        // sum of divisors of num1, 
        // so only the num that equals 
        // to sum of divisors of num1
        // is a nominee for num1.
  
        /* This if is for not to 
        make a duplication of the 
        nums, because if sum1 is 
        smaller than num1, this 
        means that we have already 
        checked the smaller one.*/
        if (sum1 > num1)
        {
            int num2 = sum1 - 1;
            int sum2 = 1;
            for (int j = 2; j * j <= num2; j++) 
            {
                if (num2 % j == 0) 
                {
                    sum2 += j;
                    if (j * j != num2)
                        sum2 += num2 / j;
                }
            }
  
        // checks if the sum divisors
        // of num2 is equal to num1.
            if (sum2 == num1 + 1) 
                Console.WriteLine("(" + num1 +
                           ", " + num2 + ")");
        }
    }
    }
  
    // Driver code
    public static void Main()
    {
    int n = 10000; 
    BetrothedNumbers(n);
    }
}
  
// This code is contributed by nitin mittal.

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PHP

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<?php
// PHP program to find Betrothed number pairs
// such that one of the numbers is smaller than
// a given number n.
  
function BetrothedNumbers($n)
{
    for ( $num1 = 1; $num1 < $n; $num1++) {
  
        // Calculate sum of num1's divisors
        // 1 is always a divisor
        $sum1 = 1; 
  
        // i=2 because we don't want to include
        // 1 as a divisor. 
        for ( $i = 2; $i * $i <= $num1; $i++) 
        {
            if ($num1 % $i == 0) {
                $sum1 += $i;
  
                // we do not want to include 
                // a divisor twice
                if ($i * $i != $num1)
                    $sum1 += $num1 / $i;
            }
        }
  
        // Now check if num2 is the sum of
        // divisors of num1, so only the num 
        // that equals to sum of divisors of 
        // num1 is a nominee for num1.
  
        /* This if is for not to make a 
            duplication of the nums, because 
            if sum1 is smaller than num1, this 
            means that we have already checked 
            the smaller one.*/
        if ($sum1 > $num1)
        {
            $num2 = $sum1 - 1;
            $sum2 = 1;
            for ($j = 2; $j * $j <= $num2; $j++) 
            {
                if ($num2 % $j == 0) {
                    $sum2 += $j;
                    if ($j * $j != $num2)
                        $sum2 += $num2 / $j;
                }
            }
      
            // checks if the sum divisors of 
            // num2 is equal to num1.
            if ($sum2 == $num1+1) 
                echo"(",$num1," ",$num2,")\n";
        }
    }
}
  
    // Driver code
    $n = 10000; 
    BetrothedNumbers($n);
      
// This code is contributed by anuj_67.
?>

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Output :

(48, 75)
(140, 195)
(1050, 1925)
(1575, 1648)
(2024, 2295)
(5775, 6128)
(8892, 16587)
(9504, 20735)

This article is contributed by Shlomi Elhaiani. 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.

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Improved By : nitin mittal, vt_m