I don't think the quality of content here has been as high as I would have liked. Over on lemmy.world/c/games, the moderation and post/comment quality are well below below what I would have expected from /r/Games in its glory days. For example, all the highest voted comments on the Starfield impressions thread are karma-whoring single sentence meme responses about pre-orders, "patient gamers", or piracy, all completely off-topic for an impressions thread.
"Arithmancy" is their name for math classes and is mentioned several times throughout the books. It is one of Hermione's favorite subjects.
At one point, the real world evil witch that is JK Rowling suggested that Arithmancy is like dviniation, but with math, saying they use numbers to predict the future. I take this to mean that the wizarding community discovered calculus independently from the rest of the world and mistook it for a new form of magic.