When math textbooks need an example of a right triangle, they frequently use a triangle with sides of length 3, 4, and 5, since the numbers work out so nicely: by the Pythagorean theorem. If that gets tiresome, 12, 5, 13 might be used: . Clearly, multiplies of these numbers work also, e.g. [...]

This post is to give some background about the constant e. Math students normally encounter e (2.7182818284590452…) in their Precalculus chapter on exponentials and logarithms, and they often wonder where this rather odd number comes from, and what is special about it.