using System;

using System.Text.RegularExpressions;

​

namespace Rextester

{

    public class Program

    {

        public static void Main(string[] args)

        {

            var rtn = "226078036";

            Console.WriteLine(IsValid(rtn));

        }

         public static bool IsValid(object value)

        {

            Regex regex = new Regex("^[0-9]{9}$");

            bool result = value is string && regex.IsMatch(value.ToString());

​

            if(result)

            {

                var stringValue = value as string;

                int check = 0;

                for (int index = 0; index < 3; index++)

                {

                    int pos = index * 3;

                    check += (int)Char.GetNumericValue(stringValue.ToCharArray()[pos]) * 3;

                    check += (int)Char.GetNumericValue(stringValue.ToCharArray()[pos + 1]) * 7;

                    check += (int)Char.GetNumericValue(stringValue.ToCharArray()[pos + 2]);

                }

                result = check != 0 && check % 10 == 0;

            }

            return result;

        }

    }

}