Generate Primes - Fast

generatePrimesFast.cs

public static List<int> returnPrimeNumbersToN(int n)
{
    List<int> primeNumbers = new List<int>();
    primeNumbers.Add(2);
    primeNumbers.Add(3);

    for (int i = 5; i <= n; i += 2)
    {
        bool test = true;
        int sqrt = Convert.ToInt32(Math.Sqrt(i));
        foreach (int prime in primeNumbers)
        {
            if (prime > sqrt) break;
            if (i % prime == 0)
            {
                test = false;
                break;
            }
        }
        if (test)
        {
            primeNumbers.Add(i);
        }  
    }
    return primeNumbers;
}