Napkin: Calculator and Notepad is a very simple to use application, good to have on hand for disposable accounts and small notes.
The intuitive interface containing only the essentials: access to the keyboard and the basic symbols of a pocket calculator. Just open the app, do the math or notes right now and leave.
The content is saved automatically, so don't worry that you won't miss anything in the meantime. The document accumulates the information it adds, but at any time you can also delete what is going on and start from scratch.
Graphically, there is another option for the user: to write in day or night mode.
In addition, Napkin is free and available from the Play Store for Android devices.