I am looking for books and/or monographs specifically about perfect numbers and related topics, where I could find proofs of results about them.
An example that I have in mind for such a book is Song Y. Yan's Perfect, Amicable, and Sociable Numbers: A Computational Approach.
However, this book's emphasis is on amicable numbers rather than perfect numbers per se. I was wondering if there was a book or monograph devoted specifically to the theory of perfect numbers.
PostScript: I found this NEU Math Circle handout by Oliver Knill. I would be very interested in seeing handouts/monographs/books similar to this last one.