Bertrand's theorem
theorem that, among central-force potentials with bound orbits, there are only 2 types of central-force scalar potentials such that all bound orbits are closed: inverse square and radial harmonic
en-GB/bɜːtɹændz ˈθɪəɹəm/
theorem that, among central-force potentials with bound orbits, there are only 2 types of central-force scalar potentials such that all bound orbits are closed: inverse square and radial harmonic