Find perfect numbers between an interval

Posted on Apr 8, 2020

C program to find perfect numbers within a given number of range.

A perfect number is a positive integer that is equal to the sum of its positive divisors, excluding the number itself.

For example, num = 28
Divisors of 28: 1, 2, 4, 7, 14, 28
Sum of divisors (excluding 28): 1 + 2 + 4 + 7 + 14 = 28
Sum = Original number
So, 28 is a perfect number

Some of the perfect numbers are 6, 28, 496, 8128, and 33550336, etc.

Program 

#include<stdio.h>
#include<conio.h>
void main()
{
	int i, j, sum;
    int low, high;

    printf("Enter two values of an interval\t:");
	scanf("%d%d",&low,&high);

    printf("Perfect numbers between %d and %d are: ", low, high);
    for(i=low;i<=high;i++)
    {
        sum = 0;
        for(j=1;j<i;j++)
        {
            if(i%j==0)
            {
                sum = sum + j;
            }
        }
        if(sum == i)
            printf("%d, ",i);
    }
    
    getch();
}

Output 

Enter two values of an interval :2
10000
Perfect numbers between 2 and 10000 are: 6, 28, 496, 8128,