This is a question relating to Problem 7-1 in Modern Physics (5th ed.) by Tipler and Llewellyn. Find the energies E311, E222, E321 and construct an energy-level diagram for the three-dimensional cubic well that includes the third, fourth, and fifth excited states. How are these states counted? I don't understand the sequencing for successive excited states. E111 would be the ground state, E211 would be the first excited state - I think I can guess that part. I don't know, however, how the next states are numbered E311, E222, and E321, successively.