PROJECT EULER #29

Link to Project Euler problem 29

Consider all integer combinations of a^b for 2 <= a <= 5 and 2 <= b <= 5:

2²=4, 2³=8, 2⁴=16, 2⁵=32
3²=9, 3³=27, 3⁴=81, 3⁵=243
4²=16, 4³=64, 4⁴=256, 4⁵=1024
5²=25, 5³=125, 5⁴=625, 5⁵=3125

If they are then placed in numerical order, with any repeats removed, we get the following sequence of 15 distinct terms:

4, 8, 9, 16, 25, 27, 32, 64, 81, 125, 243, 256, 625, 1024, 3125

How many distinct terms are in the sequence generated by a^b for 2 <= a <= 100 and 2 <= b <= 100?

using System;
using System.Collections.Generic;

namespace project_euler
{
   class Program
   {
       static void Main()
       {
           //Problem 29
           DateTime start = DateTime.Now;
           var uniques = new List<string>();
           for (int a = 2; a <= 100; a++)
           {
               BigInt n = new BigInt(a);
               for (int b = 2; b <= 100; b++)
               {
                   n *= a;
                   string s = n.ToString();
                   if (!uniques.Contains(s))
                       uniques.Add(s);
               }
           }
           Console.WriteLine(uniques.Count);
           TimeSpan time = DateTime.Now - start;
           Console.WriteLine("This took {0}", time);
           Console.ReadKey();
       }
   }
}