I got two different quantum numbers for the same problem: Hydrogen atom without any interaction.
Then, my energy is $$ E_n = -\frac{R_y}{n^2} $$ with the quantum number $n = 1, 2, 3, ....$
In another version it is $$ E_{n_r} = -\frac{R_y}{(n_r+l+1)^2} $$$$ E_{n_r} = -\frac{R_y}{(n_r+\ell+1)^2} $$ with the quantum number $n_r = n - l -1$$$n_r = n - \ell -1$.
Unfortunately, there is no explanation why it uses $n_r$ in the second formula and what the difference physically is between $n$ and $n_r$. I guess the index stands for the quantum number due to the radial part of the wave function $R_{nl}$$R_{n\ell}$ but I am confused because it works totally fine with $n$.
Is there any explanation written somewhere or can anybody explain?