Euclid Euler Theorem

According to Euclid Euler Theorem, a perfect number which is even, can be represented in the form (2^n - 1)*(2^n / 2) )) where n is a prime number and 2^n - 1 is a Mersenne prime number. It is a product of a power of 2 with a Mersenne prime number. This theorem establishes a connection between a Mersenne prime and an even perfect number.

Some Examples (Perfect Numbers) which satisfy Euclid Euler Theorem are:

6, 28, 496, 8128, 33550336, 8589869056, 137438691328

Explanations:
1) 6 is an even perfect number.
So, is can be written in the form 
(22 - 1) * (2(2 - 1)) = 6
where n = 2 is a prime number and 2^n - 1 = 3 is a Mersenne prime number.

2) 28 is an even perfect number.
So, is can be written in the form 
(23 - 1) * (2(3 - 1)) = 28
where n = 3 is a prime number and 2^n - 1 = 7 is a Mersenne prime number.

3) 496 is an even perfect number.
So, is can be written in the form 
(25 - 1) * (2(5 - 1)) = 496
where n = 5 is a prime number and 2^n - 1 = 31 is a Mersenne prime number.

Approach(Brute Force):

Take each prime number and form a Mersenne prime with it. Mersenne prime = 2^n - 1 where n is prime. Now form the number (2^n – 1)*(2^(n – 1)) and check if it is even and perfect. If the condition satisfies then it follows Euclid Euler Theorem.

C++

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// CPP code to verify Euclid Euler Theorem
#include <bits/stdc++.h>
using namespace std;
  
#define show(x) cout << #x << " = " << x << "\n";
  
bool isprime(long long n)
{
    // check whether a number is prime or not
    for (int i = 2; i * i <= n; i++)
        if (n % i == 0)
            return false;
    return false;
}
  
bool isperfect(long long n) // perfect numbers
{
    // check is n is perfect sum of divisors
    // except the number itself = number
    long long s = -n;
    for (long long i = 1; i * i <= n; i++) {
  
        // is i is a divisor of n
        if (n % i == 0) {
            long long factor1 = i, factor2 = n / i;
            s += factor1 + factor2;
  
            // here i*i == n
            if (factor1 == factor2)
                s -= i;
        }
    }
    return (n == s);
}
  
int main()
{
    // storing powers of 2 to access in O(1) time
    vector<long long> power2(61);
    for (int i = 0; i <= 60; i++)
        power2[i] = 1LL << i;
  
    // generation of first few numbers
    // satisfying Euclid Euler's theorem
  
    cout << "Generating first few numbers "
            "satisfying Euclid Euler's theorem\n";
    for (long long i = 2; i <= 25; i++) {
        long long no = (power2[i] - 1) * (power2[i - 1]);
        if (isperfect(no) and (no % 2 == 0))
            cout << "(2^" << i << " - 1) * (2^(" 
                << i << " - 1)) = " << no << "\n";
    }
    return 0;
}

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Java

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// Java code to verify Euclid Euler Theorem
class GFG 
{
    static boolean isprime(long n)
    {
        // check whether a number is prime or not
        for (int i = 2; i * i <= n; i++) 
        {
            if (n % i == 0
            {
                return false;
            }
        }
        return false;
    }
  
    static boolean isperfect(long n) // perfect numbers
    {
        // check is n is perfect sum of divisors
        // except the number itself = number
        long s = -n;
        for (long i = 1; i * i <= n; i++) 
        {
  
            // is i is a divisor of n
            if (n % i == 0
            {
                long factor1 = i, factor2 = n / i;
                s += factor1 + factor2;
  
                // here i*i == n
                if (factor1 == factor2) 
                {
                    s -= i;
                }
            }
        }
        return (n == s);
    }
  
    // Driver Code
    public static void main(String[] args) 
    {
        // storing powers of 2 to access in O(1) time
        long power2[] = new long[61];
        for (int i = 0; i <= 60; i++)
        {
            power2[i] = 1L << i;
        }
  
        // generation of first few numbers
        // satisfying Euclid Euler's theorem
        System.out.print("Generating first few numbers "
                         "satisfying Euclid Euler's theorem\n");
        for (int i = 2; i <= 25; i++) 
        {
            long no = (power2[i] - 1) * (power2[i - 1]);
            if (isperfect(no) && (no % 2 == 0)) 
            {
                System.out.print("(2^" + i + " - 1) * (2^("
                                 i + " - 1)) = " + no + "\n");
            }
        }
    }
  
// This code is contributed by PrinciRaj1992

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C#

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// C# code to verify Euclid Euler Theorem
using System;
using System.Collections.Generic;
      
class GFG 
{
    static Boolean isprime(long n)
    {
        // check whether a number is prime or not
        for (int i = 2; i * i <= n; i++) 
        {
            if (n % i == 0) 
            {
                return false;
            }
        }
        return false;
    }
  
    static Boolean isperfect(long n) // perfect numbers
    {
        // check is n is perfect sum of divisors
        // except the number itself = number
        long s = -n;
        for (long i = 1; i * i <= n; i++) 
        {
  
            // is i is a divisor of n
            if (n % i == 0) 
            {
                long factor1 = i, factor2 = n / i;
                s += factor1 + factor2;
  
                // here i*i == n
                if (factor1 == factor2) 
                {
                    s -= i;
                }
            }
        }
        return (n == s);
    }
  
    // Driver Code
    public static void Main(String[] args) 
    {
        // storing powers of 2 to access in O(1) time
        long []power2 = new long[61];
        for (int i = 0; i <= 60; i++)
        {
            power2[i] = 1L << i;
        }
  
        // generation of first few numbers
        // satisfying Euclid Euler's theorem
        Console.Write("Generating first few numbers "
                      "satisfying Euclid Euler's theorem\n");
        for (int i = 2; i <= 25; i++) 
        {
            long no = (power2[i] - 1) * (power2[i - 1]);
            if (isperfect(no) && (no % 2 == 0)) 
            {
                Console.Write("(2^" + i + " - 1) * (2^("
                                i + " - 1)) = " + no + "\n");
            }
        }
    }
}
  
// This code is contributed by Rajput-Ji

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PHP

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<?php
// PHP code to verify 
// Euclid Euler Theorem
  
// define show(x) 
// cout << #x << " = " << x << "\n";
  
function isprime($n)
{
    // check whether a number
    // is prime or not
    for ($i = 2; $i * $i <= $n; $i++)
        if ($n % $i == 0)
            return false;
    return false;
}
  
function isperfect($n) // perfect numbers
{
    // check is n is perfect sum 
    // of divisors except the 
    // number itself = number
    $s = -$n;
    for ($i = 1; 
         $i * $i <= $n; $i++) 
    {
  
        // is i is a divisor of n
        if ($n % $i == 0) 
        {
            $factor1 = $i;
            $factor2 = $n / $i;
            $s += $factor1 + $factor2;
  
            // here i*i == n
            if ($factor1 == $factor2)
                $s -= $i;
        }
    }
    return ($n == $s);
}
  
// Driver code
  
// storing powers of 2 to 
// access in O(1) time
$power2 = array();
for ($i = 0; $i <= 60; $i++)
    $power2[$i] = 1<< $i;
  
// generation of first few 
// numbers satisfying Euclid 
// Euler's theorem
echo "Generating first few numbers "
     "satisfying Euclid Euler's theorem\n";
       
for ($i = 2; $i <= 25; $i++) 
{
    $no = ($power2[$i] - 1) * 
          ($power2[$i - 1]);
    if (isperfect($no) && 
                 ($no % 2 == 0))
        echo "(2^" . $i . " - 1) * (2^("
                     $i . " - 1)) = "
                     $no . "\n";
}
  
// This code is contributed by mits
?>

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Output:

Generating first few numbers satisfying Euclid Euler's theorem
(2^2 - 1) * (2^(2 - 1)) = 6
(2^3 - 1) * (2^(3 - 1)) = 28
(2^5 - 1) * (2^(5 - 1)) = 496
(2^7 - 1) * (2^(7 - 1)) = 8128
(2^13 - 1) * (2^(13 - 1)) = 33550336
(2^17 - 1) * (2^(17 - 1)) = 8589869056
(2^19 - 1) * (2^(19 - 1)) = 137438691328

Explanation of the outputs are provided in the the explanations to the examples above.

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