PrimeTool

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

namespace FindPrimes
{
   public static class PrimeTool
    {
       public static bool IsPrime(ulong candidate)
       {
           // Test whether the parameter is a prime number. Source: http://www.dotnetperls.com/prime
           if ((candidate & 1) == 0)
           {
               if (candidate == 2)
               {
                   return true;
               }
               else
               {
                   return false;
               }
           }
           // Note:
           // ... This version was changed to test the square.
           // ... Original version tested against the square root.
           // ... Also we exclude 1 at the end.
           for (ulong i = 3; (i * i) <= candidate; i += 2)
           {
               if ((candidate % i) == 0)
               {
                   return false;
               }
           }
           return candidate != 1;
       }
    }
}