\documentclass[12pt,a4paper]{article}
\begin{document}
\begin{table}[ht]
\begin{center}
\caption{All statistics are based on contigs of size $\geq$ 500 bp, unless otherwise noted (e.g., "\# contigs ($\geq$ 0 bp)" and "Total length ($\geq$ 0 bp)" include all contigs).}
\begin{tabular}{|l*{21}{|r}|}
\hline
Assembly & \# contigs ($\geq$ 0 bp) & \# contigs ($\geq$ 1000 bp) & \# contigs ($\geq$ 5000 bp) & \# contigs ($\geq$ 10000 bp) & \# contigs ($\geq$ 25000 bp) & \# contigs ($\geq$ 50000 bp) & Total length ($\geq$ 0 bp) & Total length ($\geq$ 1000 bp) & Total length ($\geq$ 5000 bp) & Total length ($\geq$ 10000 bp) & Total length ($\geq$ 25000 bp) & Total length ($\geq$ 50000 bp) & \# contigs & Largest contig & Total length & GC (\%) & N50 & N75 & L50 & L75 & \# N's per 100 kbp \\ \hline
contigs & 94901 & 75645 & 7696 & 2673 & 656 & 229 & 249196148 & 235429846 & 98048950 & 64320930 & 35011522 & 20618873 & 89716 & 366762 & 248136525 & 56.48 & 3489 & 1833 & 14029 & 39181 & 0.00 \\ \hline
\end{tabular}
\end{center}
\end{table}
\end{document}
