Сумма рядов

#include <iostream>
#include <cmath>
#include <cstdlib>
 
using namespace std;
 
const int m = 1000000;
const int index = 6;
const float eps = 0.001;
 
double f_first, f_second, factorial, sum, x, a;
int main() {
    f_first = 0;
    f_second = 1;
    sum = 0;
    factorial = 1;
    for(int i = 3; a <= eps; i++){
        x = f_second;
        f_second += f_first;
        f_first = x;
 
        factorial *= i-1;
        a = (f_second*pow(index, i)*sqrt(i))/factorial;
        sum += a; // f2 * 6^i * sqrt(i) / x;  x = (i-2)!*(i-1)
        cout << "Count iteration: " << i << endl;
        if(sum > m) break;
    }
 
    cout << "Your sum: " << sum << "\n";
    system("pause");
    return 0;
}

double myPow(double x,int power)
{
double result=x;
for (int i=2;i<power+1;i++)
{
    result*=x;
}
return result;
}