I’ll give the background on this sometime, but I have a need for a weird thing and I don’t know if it exists or not. I need a calculator that basically only calculates one formula whenever asked. I put in a number, it applies the formula and spits a number back out at me. I need this to be portable, so not an app on a computer or tablet. Ideally it would be a standalone bit of consumer electronics. If an app is the only solution, I can try to find a cheap Android device somewhere (I think I have some old ones lying around).

Does something like this exist?