task3

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

int main()
{
     unsigned int sum;
    int n,a1, q;
    scanf_s("%d", &n);
    a1 = 1;
    q = 2;
    sum = a1*(1 - pow(q,n) )/ (1 - q);
    
    printf("n=:%d,sun=%u\n", n, sum);

    return 0;
}

不能，n取64时，计算结果数据过大，超出无符号整形的范围