Discrete Logarithm Notation Im studying for my final, and some of the practice problems that I have found have discrete logarithms in this notation $L_n(p)$. 

What does this notation equate to? 

For example:
$\log_n(x)$ means the base-$n$ logarithm of $x$. It returns a value $y$ such that $n ^ y = x$.

Since you're working with discrete logarithms, the base will probably be the generator $g$ for your group.

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$L_{13}(x)$ appears to be a shorthand way of writing the above. The only way to find out otherwise would be to consult the notation definitions from the paper (or author) if possible, because it could mean something else entirely or something more specific.