Answer
$1,866,442,158,555,975$
Work Step by Step
Recall: ${n\choose j}=\dfrac{n!}{(n-j)!j!}$.
Hence, using the formula above and a calculator gives
\begin{align*} \require{cancel}
{55\choose 23}&=\dfrac{55!}{(55-23)!23!}\\ &=\dfrac{55!}{32!23!}\\ &=1,866,442,158,555,975\end{align*}