How to Put Numbers in a Book

I love it when I see a series and I can tell, like I said very visual like they're all part of the same. We had talked about putting numbers in a book. Do you ever see that or is that anything, do you see that currently or have you seen that really ever that people put like numbers in there? Just curious for the romance genre. Or any other if you see it in one genre and not the other. Here are my books. Okay. So, that's awesome. Right. Yeah, because we, I do I love it when she says 'Here are my books' It's just my observation. This is what I've kind of been saying I