Did you know your browser includes a powerful scripting language called Javascript and that you can open up a "Console" (command-line) tab in any window to evaluate expressions in that language? 

To access it, press F12 or use the menu options:

• Web Developer > Web Console (from Firefox)
• More Tools > Developer Tools > Console (from Chrome or Edge)

Then you can type in expressions such as:

(0x10_0000+4*2**20).toString(16) 

and have the result displayed.  In this case it's the result of adding 0x100000 to four times "2 to the power 20" (4 × 1 MB) and converting the result to hexadecimal (base 16).

You can use the prefix 0x for hexadecimal and 0b for binary.  You can use underscores in numeric literals as separators.  The usual arithmetic operators (+, -, *, /) are available as well as C-like bitwise operators and many more.