http://projecteuler.net/problem=21 [Answer:31626]

 

#include <iostream>using namespace std;int main(){    const int N = 10000;    int nDivisorsDum[N];    fill( nDivisorsDum, nDivisorsDum+N, 0 );        for ( int i = 1; i < N; ++i )    {        for ( int j = i + i; j < N; j += i )        {            nDivisorsDum[j] += i;        }    }    int nSum = 0;    for ( int i = 1; i < N; ++i )    {        if ( nDivisorsDum[i] < N && nDivisorsDum[i] != i && nDivisorsDum[nDivisorsDum[i]] == i )        {            nSum += i;        }    }    cout << nSum << endl;    return 0;}