PROJECT EULER #46

Link to Project Euler problem 46

It was proposed by Christian Goldbach that every odd composite number can be written as the sum of a prime and twice a square.

9 = 7 + 2x1²
15 = 7 + 2x2²
21 = 3 + 2x3²
25 = 7 + 2x3²
27 = 19 + 2x2²
33 = 31 + 2x1²

It turns out that the conjecture was false.

What is the smallest odd composite that cannot be written as the sum of a prime and twice a square?

using System;

namespace project_euler
{
class Program
{
    static void Main()
    {
        //Problem 46
        DateTime start = DateTime.Now;
        bool test=false;
        for (int i = 3; i < 1000000; i++)
        {
            if (!IsPrime(i) && i % 2 != 0)
            {
                for (int j = 1; j <= i - 2; j += 2)
                {
                    if (IsPrime(j))
                    {
                        test = false;
                        double k = i - j;
                        if (k % 2 == 0)
                        {
                            k = k / 2;
                            if (Math.Sqrt(k) == Math.Floor(Math.Sqrt(k)))
                            {
                                test = true;
                                break;
                            }
                        }
                    }
                }
                if (!test)
                {
                    Console.WriteLine(i);
                    break;
                }
            }
        }
        TimeSpan time = DateTime.Now - start;
        Console.WriteLine("This took {0}", time);
        Console.ReadKey();
    }
    public static bool IsPrime(int n)
    {
        if (n < 2)
            return false;
        if (n == 2)
            return true;
        for (long i = 2; i <= Math.Sqrt(n); i++)
            if (n % i == 0)
                return false;
        return true;
    }
}
}

Triple-click for answer: 5777