CG求数列的前十项和

#include<bits/stdc++.h>
using namespace std;
int main(){
	double num=0;
	double sum=0;
	for(int n=1;n<=10;n++){
		    int i=2;
			double a=pow(i,n);
			double b=a-1;
			num=b/a;
			sum += num;
		}
	cout<<sum<<endl;
	return 0;
	}