I'm seeing a version of the potential as -Ze^2/4πεr. My question is what exactly does the Ze^2 refer to? I think the e^2 is supposed to represent the proton and the neutron, and the Z is supposed to represent the number of protons, but I'm not sure how to read it. Does e refer to the charge sign or to the actual value of the charge in coulombs? And Z seems to multiply the whole thing, both the proton and electron together. That doesn't make sense if it's just supposed to represent how many protons there are.