错误出在了哪里，最终结果一直为10

k<=i或k<i+1，你的内层循环少计算了i=4的值

#include <iostream>

int main()
{
    int n;
    std::cin >> n;
    int s = 0;
    int t = 0;
    for (int i = 1; i <= n; i++)
    {
        t += i;
        s += t;
    }
    std::cout << s << std::endl;
    return 0;
}