I think the denominator of your \frac
expression suffers from two issues:
- a "cramped" look, i.e., the exponents are not raised much above the baseline
- first- and second-order exponents are raised to (very nearly) the same height
How to remedy these issues?
To address the first issue, switch to "uncramped" mode -- see the \ufrac
macro below.
To remedy the second issue, I suggest you switch from {n^n}^2
to n^{n^2}
. (The two forms are the same, mathematically speaking, but they are quite differnt from a typographic point of view.) That, or use parentheses to visually "enclose" the n^n
term.
Alternatively, consider switching from "standard" \frac
notation to inline-fraction notation.
Whatever else you do, please don't use the unnecessary *
multiplication symbol. If you can't do without an explicit multiplication symbol, do use \cdot
, not *
.

\documentclass{article}
%% "uncramped" \frac macro:
%% (Source: @egreg [who else?!], https://tex.stackexchange.com/a/337334/5001)
\makeatletter
\newcommand{\ufrac}[2]{%
\frac{#1}{\mathpalette\ufrac@den{#2}}}
\newcommand{\ufrac@den}[2]{#1#2}
\makeatother
\begin{document}
inline math mode, \verb+\frac+ notation
$\frac{n^n}{{2}^{2n} * {n^n}^{2}} % OP's expression
\quad
\ufrac{n^n}{2^{2n} n^{n^2}}
\quad
\ufrac{n^n}{2^{2n} (n^n)^2}$
\bigskip
display math mode, \verb+\frac+ notation
\smallskip
$\displaystyle
\frac{n^n}{2^{2n} n^{n^2}}
\quad
\ufrac{n^n}{2^{2n} n^{n^2}}
\quad
\ufrac{n^n}{2^{2n} (n^n)^2}$
\bigskip
inline-frac notation
\smallskip
$n^n/(2^{2n} n^{n^2})
\quad
n^n/(2^{2n} (n^n)^2)$
\end{document}
{\fboxrule=0pt \fbox{...}}