Algorithms

void Test()
{
    List<long> primeNumbers = new List<long>();
    primeNumbers.Add(3);
    primeNumbers.Add(5);
    DateTime stopTime = DateTime.Now + new TimeSpan(0, 10, 0);
    Console.Write("Calculating prime numbers...");
    while (DateTime.Now < stopTime)
    {
        if (primeNumbers.Count % 100 == 0)
            Console.Write(".");
        primeNumbers.Add(GetNextPrime(primeNumbers));
    }
    Console.WriteLine("Calculated " + primeNumbers.Count + " prime numbers.");
    Console.WriteLine("The largest being " + primeNumbers.Last() + ".");
}

long GetNextPrime(List<long> primeNumbers)
{
    long lastPrime = primeNumbers.Last();
    for (int i = 0; i < primeNumbers.Count - 1; i++)
    {
        long testValue = lastPrime + primeNumbers[i] - 1;
        bool fail = false;
        for (int j = 0; j < primeNumbers.Count - 1; j++)
        {
            if (testValue % primeNumbers[j] == 0)
            {
                fail = true;
                break;
            }
        }
        if (fail) continue;
        return testValue;
    }
    throw new Exception("Rule failed");
}