Betrothed numbers - GeeksforGeeks

16 Apr, 2021
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), (140, 195)

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++
Java
Python
C#
PHP
Javascript
// 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 codeint main(){    int n = 10000;    BetrothedNumbers(n);    return 0;}
// 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.
# 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 = 10000BetrothedNumbers(n) # This code is contributed by Nikita Tiwari.
// 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.
<?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.?>
<script>// Javascript program to find Betrothed number pairs// such that one of the numbers is smaller than// a given number n.function BetrothedNumbers(n){    for (let num1 = 1; num1 < n; num1++)    {         // Calculate sum of num1's divisors        let sum1 = 1; // 1 is always a divisor         // i=2 because we don't want to include        // 1 as a divisor.        for (let 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 += parseInt(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)        {            let num2 = sum1 - 1;            let sum2 = 1;            for (let j = 2; j * j <= num2; j++)            {                if (num2 % j == 0) {                    sum2 += j;                    if (j * j != num2)                        sum2 += parseInt(num2 / j);                }            }                  // checks if the sum divisors of            // num2 is equal to num1.            if (sum2 == (num1+1))                document.write(`(${num1}, ${num2})<br>`);        }    }} // Driver code    let n = 10000;    BetrothedNumbers(n); // This code is contributed by rishavmahato348.</script>
Output :  
(48, 75)
(140, 195)
(1050, 1925)
(1575, 1648)
(2024, 2295)
(5775, 6128)
(8892, 16587)
(9504, 20735)
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nitin mittal
vt_m
besupujis
rishavmahato348
number-theory
Mathematical
number-theory
Mathematical
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