Lychrel Numbers

LychrelNumbers.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Numerics;
using static System.Linq.Enumerable;
using static System.Numerics.BigInteger;
using static System.Console;

namespace LychrelNumbers
{
    class Program
    {
        private static IEnumerable<int> GetAllPositiveIntegers()
        {
            return Range(0, int.MaxValue);
        }

        private static string Revert(string text)
        {
            return new string(text.Reverse().ToArray());
        }

        private static bool IsPalindrome(BigInteger number)
        {
            var stringified = number.ToString();
            return stringified == Revert(stringified);
        }

        private static BigInteger RevertAndAdd(BigInteger number)
        {
            var stringified = number.ToString();
            var reverted = Revert(stringified);
            var revertedNumber = Parse(reverted);
            return number + revertedNumber;
        }

        private static bool IsLychrelNumber(int x)
        {
            BigInteger number = x;

            foreach (var i in Range(0, 50))
            {
                number = RevertAndAdd(number);

                if (IsPalindrome(number))
                    return false;
            }

            return true;
        }

        static IEnumerable<int> GetLychrelNumbers()
        {
            return GetAllPositiveIntegers()
                .Where(x => IsLychrelNumber(x));
        }

        static void Main(string[] args)
        {
            var threshold = 100000;

            var lychrelNumbersUnderThreshold = GetLychrelNumbers()
                .TakeWhile(x => x < threshold)
                .ToList();

            foreach (var lychrelNumber in lychrelNumbersUnderThreshold)
            {
                WriteLine(lychrelNumber);
            }

            WriteLine($"There's { lychrelNumbersUnderThreshold.Count } Lychrel Numbers under { threshold }.");
        }
    }
}