C-Programs For Perfect Number

Definition of perfect number or What is perfect number? 

A perfect number is a positive integer that is equal to the sum of its proper positive divisors, i.e., the sum of its positive divisors excluding the number itself. It is also known as aliquot sum. Equivalently, a perfect number is a number that is half the sum of all of its positive divisors including itself. 

For example 6 is perfect number since divisor of 6 are 1, 2 and 3.  Sum of its divisor is

1 + 2+ 3 =6

Note: 6 is the smallest perfect number.

Next perfect number is 28 since 1+ 2 + 4 + 7 + 14 = 28

Some more perfect numbers: 496 , 8128 , 33550336 , 8589869056 , 137438691328  

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C program to check whether the number is a perfect 

#include<stdio.h>

#include<conio.h>
int main()

{

  int n,i=1,sum=0;

  clrscr();

  printf("Enter a number: ");

  scanf("%d",&n);

  while(i<n)

  {

    if(n%i==0)

      sum=sum+i;

      i++;

  }

  if(sum==n)

    printf("It is a perfect number");

  else

    printf("It is not a perfect number");

  return 0;

}

output:

Enter a number: 6

It is a perfect number

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 C program to find perfect numbers within a given range

#include<stdio.h> 
#include<conio.h>

int main()

{

  int n,i,sum;

  int min,max;

  clrscr();

  printf("Enter the minimum range: ");

  scanf("%d",&min);

  printf("Enter the maximum range: ");

  scanf("%d",&max);

  printf("Perfect numbers in given range is: ");

  for(n=min;n<=max;n++)

  {

    i=1;

    sum = 0;

    while(i<n)

    {

      if(n%i==0)

      {

        sum=sum+i;

      }

      i++;

    }

    if(sum==n)

      printf("%d ",n);

  }

  return 0;

}

output:

Enter the minimum range: 1

Enter the maximum range: 20

Perfect numbers in given range is: 6

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C program to print perfect numbers from 1 to 100

#include<stdio.h>

#include<conio.h>

int main()

{

  int n,i,sum;

  clrscr();

  printf("Perfect numbers are: ");

  for(n=1;n<=100;n++)

  {

    i=1;

    sum = 0;

    while(i<n)

    {

      if(n%i==0)

           sum=sum+i;

          i++;

    }

    if(sum==n)

    printf("%d ",n);

  }

  return 0;

}

 Output:

Perfect numbers are: 6 28