e(~2.71828182846) is the base of the natural logarithm. This is one of its definitions.
I would consider it as a place to put all the pens on my desk.
Any suggestion will be appreciated.

This thing was (partially) made with Tinkercad. Edit it online https://tinkercad.com/things/1vZSF3ch0x4

I made the space behind about 16cm(~6+1/4 inches) wide. Scale it up when needed.