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-...