problem from Softuni

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
     public  class Program
    {
        public static void Main(string[] args)
        {
            HashSet<int>normalNumbers=new HashSet<int>();
            StringBuilder sb=new StringBuilder();
            for(int i=10;i<100;i++)
            {
                for(int j=10;j<100;j++)
                {
            int m=i;
            int n=j;

            char[]reverseTwo=n.ToString().ToCharArray();
            Array.Reverse(reverseTwo);
            string getIntTwo=string.Concat(reverseTwo);

            char[]reverse=m.ToString().ToCharArray();
            Array.Reverse(reverse);
            string getInt=string.Concat(reverse);

            int b=int.Parse(getInt);
            int a=int.Parse(getIntTwo);
            int mXnResult=m*n;
            int aXbResult=a*b;

            bool Even=mXnResult==aXbResult;

                    if(Even)
                    {
                        normalNumbers.Add(n);
                        normalNumbers.Add(m);
                        normalNumbers.Add(a);
                        normalNumbers.Add(b);
                        string evenPairs=string.Format("{0}*{1}={2}*{3} ={4}",n,m,a,b,aXbResult);
                        sb.AppendLine(evenPairs);

                    }

                }
            }
            Console.WriteLine(string.Join(" ",normalNumbers.OrderBy(x=>x)));
            Console.WriteLine();
            Console.WriteLine(sb.ToString().TrimEnd());


        }

    }