有知道的人教我下

//用C#写一个程序，计算s=1+(1+2)+(1+2+3)+...(1+2+3+4+....+n)n=10
        static int AddSum(int n)
        {
            int sum = 0;
            for (int i = 1; i <= n; ++i)
            {
                for (int j = 1; j <= i; ++j)
                {
                    sum += j;
                }
            }
            return sum;
        }
 
        static int AddSumFormula(int n)
        {
            int sum = 0;
            for (int i = 1; i <= n; ++i)
            {                 
                sum += (1 + i)*i/ 2;
            }
            return sum;
        }