Sum of series in c++

#include<iostream>
#include<conio.h>
#include<math.h>
using namespace std;
int main()
{

double numb;
double sum=0;
int i;
cout << "Enter number:";
cin >> numb;
for(i=2;i<numb ;i++)
{


sum=sum+pow(numb,i);
cout << sum<<",";
}
getch();
return 0;
}