using System;

using System.Text.RegularExpressions;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

            var content = "zf3kabxcde224lkzf3mabxc51+crsdtzf3nab=";

            var patternLength = 3;            

            var patterns = new HashSet<string>();                   

​

            for (int i = 0; i < content.Length - patternLength + 1; i++)

            {

                var pattern = content.Substring(i, patternLength);                

                var Occurrence = Regex.Matches(content, pattern.Replace("+", @"\+")).Count;

                if (Occurrence > 1 && !patterns.Contains(pattern))

                {

                    Console.WriteLine(pattern + " : " + Occurrence);

                    patterns.Add(pattern);

                }               

            }

    }

}