I love Numberphile, and I love this kind of Numberphile specifically: here, starting from small numbers using ideas and operations that are extremely easy to understand and (at some scale) iterate by hand, is a wild unsolved problem absolutely beyond the reach of our current mathematical or computational capacities:

https://m.youtube.com/watch?v=OtYKDzXwDEE&pp=ugUEEgJlbg%3D%3D

An amazing thing about 276 - Numberphile

YouTube

I think the thing I love most about this is that is, like so much involving prime numbers and factorization, an extremely powerful brand of catnip for amateur crank mathematicians such as myself. You can _kind of see_ the patterns there! There are the barest hints of a _lot_ of subtle structure. The secret must be within our grasp!

I mean, does this not look _just like_ the 3x+1 problem, turned on its head? Almost? Maybe?

And yet.... and yet....

C. S. Lewis once described The Occult as a series of nested snares, symbols for symbols for symbols without ultimate referent, a machine purpose-built to be an intellectual rat hole, seducing and confusing the inquisitive mind, snaring the most inquisitive of minds that much more effectively.

But, in a very Lovecraftian way, there are things that we can find right here in nature fully capable of that, of having the shape of the occult - or rather, a true shape, aped badly by the occult.

You can see why so much of occultism falls back on the iconology of pure math disciplines, how many symbols and ceremonies are just algebraics and slow chanting, how far you can take a cult with some graph theory and a disused cathedral. Adding the ill-mixed flavor of the true incomprehensible infinite to your game of cryptosefirotic rune-scrabble in an exercise in semiotic aura farming is a temptation that has no name, that we respond to with a reflex older than language.
@mhoye 'Cryptosefirotic' almost had me inhaling my tea. Watch where you point that thing, please; it's almost certainly loaded. (Honest question: do you expect your audience to parse the word on their own, or should we just accept the dictionary-diving as a side-quest along the journey?)
@dubious_dragon At this point I just have to trust my audience to know they have to buckle their seatbelts and keep their hands inside the ride.
@mhoye That's entirely fair. It's been a long time since I've stretched my morphological horizons that much; it's probably good for me.