using System;

using System.Collections.Generic;

using System.Numerics;

using NUnit.Framework;          

​

public class Program

{

    public static void Main()

    {

        Assert.AreEqual(new BigInteger[] { 1, 2, 4, 8, 16 }, PowersOfTwo(4));

    }

  public static BigInteger[] PowersOfTwo(int n)

  {

     int pow=1, count = 1;

    List<BigInteger> ans= new List<BigInteger>();

      BigInteger ans2 = 1;

      ans.Add(ans2);

      while (ans2 <= n){

          ans2 = (BigInteger) Math.Pow(2.0, pow);

          ans[count] = ans2;

          pow +=2;

          count++;

      }

    return ans.ToArray();

  }

​

}