C#之递推问题

//求下列数列的前20项
//     *  0                       n=0
//     *  1                       n=1
//y[n]=*  2                       n=2
//     *  y[n-1]+2*y[n-2]+y[n-3]  n>2
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace test
{
    class Program
    {
        static void Main()
        {
            int[] y = new int[20];    //C#中的动态分配
            y[0] = 0;
            y[1] = 1;
            y[2] = 2;
            for (int i = 3; i <20; i++)
            {
                y[i] = y[i - 1] + 2 * y[i - 2] + y[i - 3];
            }
            foreach (int i in y)
            {
                Console.WriteLine(i);
            }

        }
    }
}