using System;

public class Program

{

    public static void Main()

    {

            var dict = new Dictionary<int, string>();

            var serials = new List<string>();

            string path = "C:\\Users\\User\\Desktop\\serials.txt";

            string str1 = "000000";

            string str2 = "157247";

            int key = 0;

            try

            { 

                using(StreamReader strReader = new StreamReader(path))

                {

                    while(!strReader.EndOfStream)

                    { 

                        serials.Add(strReader.ReadLine());

                    }

                    strReader.Close();

                }

​

                var sorted = from str in serials orderby str ascending select str;

​

                foreach (var str in sorted)

                {

                    dict.Add(key++, str);

                }

​

                var key1 = from keyValue in dict where str1 == keyValue.Value select keyValue.Key;

                var key2 = from keyValue in dict where str2 == keyValue.Value select keyValue.Key;

                var filter = from str in dict where str.Key <= key2.ToArray()[0] && str.Key >= key1.ToArray()[0] select str.Value;

                var final = filter.ToList();

            }

            catch (Exception ex)

            {

                Console.WriteLine(ex);

            }

​

    }

}