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The separation between the 1p3/2 and 1p1/2 single-neutron energies outside of the N = 20 isotones decreases by about 1 MeV between 41Ca and 35Si. This raises the question: what mechanism is responsible for this decrease? I review the experimental data on proton occupancies and neutron single-particle energies at N = 20 and 21, respectively, and discuss the change in separation of the 1p spin-orbit partners in terms of the postulated bubble nature of 34Si, the influence of weak binding on single-particle excitations, and two-body effects.