Why does e = 2.71828183? Or how e SHOULD have been discovered.

This is an interesting exercise to do with higher level mathematical students - it shows them that the value of $e$ can be derived purely from it's differential properties.

So we start with the fundamental property of $e$, that $D(e^x)_x = e^x$.
In short, we're looking for the identity function of differentiation - what function stays unchanged.
(As noted in previous posts, I'm using a differential format similar to sagemath's default format.)