Yes it was, and thanks for the tip, Pajamaman.
I've searched the web for e-ink and Android, but Onyx didn't show up. I am adding some links here for future reference. This is their
website, this is the e-book reader
with the newest version of Android (Marshmallow) and here's a store
selling that e-book reader.
What I would really like to get, and I doubt an Android Marshmallow tablet would do, is to have a split screen with my math book (e-pub) covering the top and an area at the bottom where I could write. So I could do without relying on a physical textbook and a physical notebook.