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 public class factorial
   {
       int n;
       public void ser()
       {
           double f, sum = 2, res = 1, up = 2;

           Console.WriteLine("\n\t\tSeries = 2/1! + 4/3! + 6/5! + 8/7! + 10/9! + . . . + n/(n-1)!");
           Console.WriteLine();
           Console.Write("\n\t\tEnter ending point : ");
           n = Convert.ToInt16(Console.ReadLine());

           for (int i = 2; i <= n; i++)
           {
               if (i % 2 == 1)
               {
                   f = 1;
                   for (int x = i; x > 0; x--)
                   { f = f * x; }
                   up = up + 2;
                   res = up / f;
                   sum = sum + res;
               }
           }
           Console.WriteLine("\n\t\tSum : {0}\n", sum);
           Console.WriteLine();
       }
   }