Thanks. Good site:
Looking at the meaning of this equation, it says that electrons are allowed only orbits of certain (quantized) radii, where n = 1, 2, 3...
This confirms the impression I got from Cramer's article. (I must admit, I skimmed over the equation.)
Actually the Bohr model is an oversimplification. However, you can envision these "orbits" as probability zones. In the case of the Hydrogen atom you get a spherical shell.
But you only have spherical shells if the orbital (l) and angular momentum (m) quantum numbers are zero, for other values of l and m you get pretty weird orbitals like lobes or rings (
click for nice pics).