如何用C#语言实现以下递归方法？

Question

  今天老师出了道题目，大大们帮实现下：
  有一单性繁殖细胞，4天后繁殖出一个新细胞，以后每天繁殖一个。依次类推，20天后有多少个细胞？
  代码如何下，麻烦大大们贴出下！

Answer 1

为什么要递归？
using System;
using System.Collections.Generic;namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            // First generate frist ear TheCell
            Chaos.Genesis();
            int timeGoes = 1;
            while (timeGoes <= 20)
            {
                Console.WriteLine("The " + timeGoes.ToString() + " Day");
                Chaos.LiveOneDay();
                Console.WriteLine("\tThe total TheCell Count is: " + Chaos.CountTheCell());
                timeGoes++;
            }            Console.WriteLine("The 20th day, total cell count is "  + Chaos.CountTheCell() + Environment.NewLine + "Press enter key quit.");
            Console.ReadLine();
        }
    }    public static class Chaos
    {
        private static int DayTick = 0;
        private static List<TheCell> AllTheCells = new List<TheCell>();
        private static List<TheCell> NewBreadedCells = new List<TheCell>();        public static void Genesis()
        {
            AllTheCells.Add(new TheCell());
        }        public static void LiveOneDay()
        {
            foreach (TheCell cell in AllTheCells)
            {
                cell.Live();
                if (cell.CanBread)
                    NewBreadedCells.Add(new TheCell());
            }
            AllTheCells.AddRange(NewBreadedCells);
            NewBreadedCells.Clear();
            
            DayTick++;
        }        public static int CountTheCell()
        {
            return AllTheCells.Count;
        }
    }    public class TheCell
    {
        int _age = 0;        public void Live()
        {
            _age++;
        }        public  bool CanBread
        {
            get { return _age > 4; }
        }
    }
}