Frankly, I have no idea (although I have written on this topic) what you are asking about.
Have a look at this webpage.
This idea is also closely related to Bell Numbers.
Now here is my rant.
I think it is rude of you to ask us to download and read unknown files. That is an easy wayout.
YOU can post the questions that you have.
Learning to post in LaTeX is relatively easy.
If you are serious about this study then you are going to be required to learn it.