gistfile1.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Diagnostics;

namespace euler12
{
    class Program
    {
        static void Main(string[] args)
        {
            Stopwatch sw = new Stopwatch();
            sw.Start();
            Console.WriteLine(calc(500));
            sw.Stop();
            Console.WriteLine("calculated in {0}",sw.Elapsed.TotalSeconds);
        }
        public static UInt64 GetNthTriangularNum(UInt64 n)
        {
           
            return n*(n+1)/2;
        }
        public static int GetNumberOfDivisors(UInt64 n)
        {
            int result = 2;
            UInt64 start = 2;
            UInt64 end = n;
            for (UInt64 i = start; i < end; i+=1)
            {
                if (n%i==0)
                {
                    start = i;
                    end = n / i;
                    result+=start==end?1:2;
                }
                
            }
            return result;
        }

       public static UInt64 calc(int max)
        {
            UInt64 i = 1;
            while (GetNumberOfDivisors( GetNthTriangularNum(i))<max)
            {
                i++;
            }
            return GetNthTriangularNum(i);
        }
        
    }
}