For any positive integer
n, let
f(n) denote the number of solutions to the Diophantine equation
\begin{eqnarray*}\frac{4}{n} = \frac{1}{x} + \frac{1}{y} + \frac{1}{z}\end{eqnarray*}
with
x, y, z positive integers. The
Erdős–Straus conjecture asserts that
f(n)\gt 0 for every
n\geq 2. In this paper we obtain a number of upper and lower bounds for
f(n) or
f(p) for typical values of natural numbers
n and primes
p. For instance, we establish that
\begin{eqnarray*}N\hspace{0.167em} {\mathop{\log }\nolimits }^{2} N\ll \displaystyle \sum _{p\leq N}f(p)\ll N\hspace{0.167em} {\mathop{\log }\nolimits }^{2} N\log \log N.\end{eqnarray*}
These upper and lower bounds show that a typical prime has a small number of solutions to the Erdős–Straus Diophantine equation; small, when compared with other additive problems, like Waring’s problem.