Creating threads in .NET

Creating a raw thread is something that mostly makes sense only when you have a long-running operation that depends on the CPU alone. As an example, let's say we want to compute prime numbers, without really caring about the possible optimizations:

public class Primes : IEnumerable<long>
{
	public Primes(long Max = long.MaxValue)
	{
		this.Max = Max;
	}
	public long Max { get; private set; }
	IEnumerator IEnumerable.GetEnumerator() => ((IEnumerable<long>)this).GetEnumerator();
	public IEnumerator<long> GetEnumerator()
	{
		yield return 1;
		bool bFlag;
		long start = 2;
		while (start < Max)
		{
			bFlag = false;
			var number = start;
			for (int i = 2; i < number; i++)
			{
				if (number % i == 0)
				{
					bFlag = true;
					break;
				}
			}
			if (!bFlag)
			{
				yield return number;
			}
			start++;
		}
	}
}

The Primes class implements IEnumerable<long> so that we can easily enumerate the prime numbers in...