C Program for Perfect Number

/*
Perfect number is a positive number, which is sum of all its positive divisors excluding original number and is equal to original number. 

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

*/

Program

#include<stdio.h>

void main()

{

  int no,i=1,sum=0;

  printf("Enter a number: ");

  scanf("%d",&no);

  while(i<no)

  {

if(no%i==0)

 sum=sum+i;

i++;

  }

  if(sum==no)

printf("%d is a perfect number",no);

  else

printf("%d is not a perfect number",no);

}

Output

Enter a number: 6

6 is a perfect number