i have tested it, and it look like working, can you say me is this look like correct, or can you advise me how to fix it?)

#include <iostream>

using namespace std;

int main()
{
    unsigned __int64 n, b, i, r, sum = 0;
    cin>>n>>b;
    for (i = 2; i <= n - 1; i++)
    {
        r = (n - 1) / i + (n - 1) % i;
        sum += r * pow(double(b - 1), double(n - i));
    }
    cout<<unsigned __int64(pow(double(b), double(n)) - pow(double(b), double(n - 1)) - sum)<<endl;
    //system("pause");
}