21_amicable_sum_of_divisors.cpp

#include <iostream>
#include <cmath>
using namespace std;

long long divisorsum(long long a)
{
    long long ans=1;
    for(int i=2;i<=pow(a,.5);i++)
    {
        if(a%i==0)
        {
            
            if(i==a/i)
            {
                ans+=i;
            }
            else
            {
                   ans+=i+(a/i);
            }
        }
    }
    return ans;
}
int main() {
	// your code goes here
	
	long long sum=0;
	long long a[10000];
	for(long long i=0;i<10000;i++)
	{
	    a[i]=divisorsum(i+1);
	   // cout<<a[i]<<endl;
	}
	
	cout<<a[219]<<endl;
	for(long long j=0;j<10000;j++)
	{
	    if(a[j]<10000){
	    if((j+1==a[a[j]-1])&&(j+1!=a[j]))
	    {
	        sum+=j+1+a[j];
	        cout<<j+1<<" "<<a[j]<<" "<<a[a[j]-1]<<endl;
	    }
	    }
	}
	cout<<sum/2;
	return 0;
}