using System;

using System.Collections.Generic;

​

public class Program

{

    public static IEnumerable<string> Get(string input)

    {

        int last = -1, first = -1;

        for (var index = 0; index < input.Length; index++)

            if (!char.IsDigit(input[index]))

            {

                if (last > 1)

                    yield return input.Substring(first, last - first + 1);

                first = last = -1;

            }

            else if (first == -1)

                first = index;

            else if (input[first] == input[index])

                last = index;

        if (last > 1)

            yield return input.Substring(first, last - first + 1);

    }

​

    public static void Main()

    {

        var input = "12346171par827here727next8number5052car";

        Console.WriteLine(string.Join(", ", Get(input)));

    }

}