An article I found interesting in a very very nerdy way:
https://chadnauseam.com/coding/random/calculator-app
Essentially, it goes through a problem I'd never thought of: you can't strictly contain any number in binary, because you can't store the infinite recursions etc, so this actually makes it really hard to write calculator apps properly at the absolute base level. And the various requirements to fully solve said problem are pretty interesting!