All my notes are in OneNote - very nice for writing formula and sketching diagrams. You can switch on graph paper if you need it as well. You can add in audio notes, get a whiteboard photo, import PDFs - personally, it’s a great all-in-one tool for me to keep my notes and ideas organized.
For the Calculator, I use Graphing Calculator Plus (even take screenshots and insert into OneNote). It’s pretty decent if you’re looking for a scientific calculator.