常用算法(C#): 计算 1+2(2次方)+3(3次方)+...+n(n次方)的值

using System;
using System.Collections.Generic;
using System.Text;

namespace ExSum
{
    class Sum
    {
        public long sum(int num)
        {
            long sum = 0;
            for (int i = 1; i <= num; i++)
            {
                long f = 1;
                //求i的i次方
                for (int j = 1; j <= i; j++)
                {
                    f *= i;
                }
                sum += f;
            }
            return sum;
        }
        static void Main(string[] args)
        {
            Console .Write("请输入一个整数:");
            int num=Convert.ToInt32 (Console.ReadLine());
            Sum s=new Sum();
            Console.WriteLine("1的1次方到{0}的{1}次方的和为{2}", num,num,s.sum (num));
        }
    }
}