5.12

#include<stdio.h>
void main(){
int a,i,b,n;
printf("There are following friendly--numbers pair smaller than3000:\n");
for(a=1;a<3000;a++)
{
for(b=0,i=1;i<=a/2;i++)
if(!(a%i))
b+=i;
for(n=0,i=1;i<=b/2;i++)
if(!(b%i))
n+=i;
if(n==a&&a<b)
printf("%4d--%4d ",a,b);
}}