gistfile1.cs

    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("Enter the number of iteractions: ");
            int count;
            if (!int.TryParse(Console.ReadLine(), out count)) count = 10;
            var value = "x";
            while (count-- > 0)
            {
                Console.WriteLine(value);
                value = value
                    .GroupBy(c => c)
                    .Select(v => string.Format("{0}{1}", v.Count(), v.Key))
                    .Aggregate((v1, v2) => string.Format("{0}{1}",v1,v2));
            }
            Console.WriteLine("Press any key to end");
            Console.ReadLine();
        }
    }