For Loop List<> Enumerable.Range(), C#

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//Rextester.Program.Main is the entry point for your code. Don't change it.
//Compiler version 4.0.30319.17929 for Microsoft (R) .NET Framework 4.5

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text.RegularExpressions;

namespace Rextester
{
    public class Program
    {
        // Letter List
        public static List<char> letter = Enumerable.Range(1, 51)
                                                    .Select(i => '\0') // null char
                                                    .ToList();
        // Index Number List
        public static List<string> indexLetter = Enumerable.Range(1, 51)
                                                    .Select(i => i.ToString()) // number
                                                    .ToList();
        // Generate Random Letter
        public static Random random = new Random();
        public static char RandomLetter()
        {
            const string text = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
            int index = random.Next(text.Length);
            return text[index];
        }
        
        
        public static void Main(string[] args)
        {
            
            // Combine Random Letter with Index Number
            for (var i = 1; i < 51; i++)
            {
                // Letter
                letter[i] = RandomLetter();

// Letter + Index Number
                indexLetter[i] = letter[i] + i.ToString();
            }
            
           // Display Letter + Index List
           Console.WriteLine(string.Join("\n", indexLetter));
        }

}
}

Show compiler warnings [ + ] Show input
Compilation time: 0,14 sec, absolute running time: 0,09 sec, cpu time: 0,08 sec, average memory usage: 13 Mb, average nr of threads: 3