The term 3/5 in the electrostatic potential energy formula for a nucleus, U_e = (3/5) * (Ze)^2 / (4πε_0 R), arises from integrating the potential energy of a uniformly charged sphere. This factor reflects the distribution of charge within the sphere, influencing the overall potential energy calculation. A similar derivation exists for gravitational binding energy, as noted on Wikipedia. Understanding this term is crucial for accurately calculating nuclear interactions. The discussion emphasizes the mathematical foundations underlying nuclear electrostatics.