# Principal quantum number

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Determines energy. This comes out directly from the resolution of the Schrödinger equation solution for the hydrogen atom where we have to set some arbitrary values of energy by separation of variables just like we have to set some arbitrary numbers when solving partial differential equations with the Fourier series. We then just happen to see that only certain integer values are possible to satisfy the equations.

This is a section about Principal quantum number!

Principal quantum number is a very important subject about which there is a lot to say.

For example, this sentence. And then another one.