Do they still offer a free license on Raspberry Pi?
Not just on Raspberry Pi, wolfram scripting engine is free and works on windows or mac too. You lose the notebook interface, but if you're just using it as a calculator, it does the job.
You can also emulate a Pi using QEMU to run Mathematica (slowly!) on other platforms, see e.g.
https://www.thelinuxvault.net/blog/how-to-run-the-raspberry-...
Not just on Raspberry Pi, wolfram scripting engine is free and works on windows or mac too. You lose the notebook interface, but if you're just using it as a calculator, it does the job.