СТРЕЛКАТА КОЯТО ИМА И ДИАГОНАЛИ :)

using System;
namespace xx.TESTER
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.Write("Enter odd numbers only [3..79]: ");
            int n = int.Parse(Console.ReadLine());

            if (n % 2 == 0)
            {
                Console.WriteLine("Your number is not odd!");
                Console.Write("Enter odd numbers only [3..79]: ");
                n = int.Parse(Console.ReadLine());
            }

            Console.WriteLine("{0}{1}{0}", new string('.', n / 2), new string('#', n));//first row

            for (int i = 0; i < n - 2; i++)
            {
                Console.WriteLine("{0}#{1}#{0}", new string('.', n / 2), new string('.', n - 2));
            }
            Console.WriteLine("{0}{1}{0}", new string('#', n / 2 + 1), new string('.', n - 2));
            for (int i = 0; i < n - 2; i++)
            {
                Console.WriteLine("{0}#{1}#{0}", new string('.', i + 1), new string('.', (2 * n - 1) - 2 - 2 * i));
            }
            Console.WriteLine("{0}#{0}", new string('.', n - 1));
        }
    }
}