pe21

#include <stdio.h>
#include <math.h>

int main()
{
  int div_sum[10000], i, j, sqrt_i, acc;

  for (i=1; i<10000; i++)
  {
    sqrt_i = sqrtf(i);
    acc = 0;

    for (j=2; j<=sqrt_i; j++)
    {
      if (i % j == 0) acc += j + i/j;
    }

    div_sum[i] = acc + 1;
  }

  acc = 0;
  for (i=1; i<10000; i++)
  {
    if (div_sum[i] < 10000)
      if (div_sum[div_sum[i]] < 10000)
        if (div_sum[div_sum[i]] == i && div_sum[i] != i)
          acc += i;
  }

  printf("%d\n",acc);
  return 0;
}