A slightly optimized prime sequence.

OddPrimeSequence.cs

public class PrimeSequence : IEnumerable<int>
{
  public IEnumerator<int> GetEnumerator()
  {
    yield return 2;
    var e = new OddPrimeEnumerator();
    while (e.MoveNext()) 
    {
      yield return e.Current;
    }
  }

  IEnumerator IEnumerable.GetEnumerator()
  {
    return GetEnumerator();
  }
}