Euler37

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApp1
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine(Enumerable.Range(10, 10000000)
                .Where(x => IsPrime(x)).Where(x =>EveryStubIsPrime(GetListOfNumbers(x))).Sum());
        }


        static bool IsPrime(int number)
        {

            if (number == 1) return false;
            if (number == 2) return true;

            var limit = Math.Ceiling(Math.Sqrt(number));

            for (int i = 2; i <= limit; ++i)
            {
                if (number % i == 0) return false;
            }
            return true;
        }

        static int RemoveFirst(int n)
        {
            var stringN = n.ToString();
            return Convert.ToInt32(stringN.Remove(0, 1));
        }
        static int RemoveLast(int n)
        {
            var stringN = n.ToString();
            return Convert.ToInt32(stringN.Remove(stringN.Length-1, 1));
        }

        static List<int> GetListOfNumbers(int n)
        {
            var listOfStubs = new List<int>() {n};
            var nn = n; //for deleting letters from left
            while ((1 < n.ToString().Length)&&(1 < nn.ToString().Length ))
            {
                n = RemoveLast(n);
                listOfStubs.Add(n);
                nn = RemoveFirst(nn);
                listOfStubs.Add(nn);
            }
            return listOfStubs;
        }

        static bool EveryStubIsPrime(List<int> stub)
        {
            return stub.All(x => IsPrime(x));
        }

    }
}