5.11

#include<stdio.h>
main(){
int i,j,s,n;
printf("请输入所选范围上限:");
scanf("%d",&n);
for(i=2;i<=n;i++)
{
s=0;
for(j=1;j<i;j++)
{
if(i%j==0)
s+=j;}
if(s==i)
printf("It is a perfect number:%d.\n",i);}}