This is binomial with n = 20, p = 1/2 and you are looking for f(10). With these values
\begin{equation*}
f(10) = \binom{20}{10} \cdot \left ( \frac{1}{2} \right )^{10} \cdot \left ( \frac{1}{2} \right )^{20-10} = \frac{46189}{262144} \approx 0.176
\end{equation*}
Note that the mean for this distribution is also 10 so one might expect 10 heads in general