Assume that protons and neutrons have equal masses. Mass of a nucleon is $1.6 \times 10^{-27} \mathrm{~kg}$ and radius of nucleus is $1.5 \times 10^{-15} \mathrm{~A}^{1 / 3} \mathrm{~m}$. The approximate ratio of the nuclear density and water density is $\mathrm{n} \times 10^{13}$. The value of $n$ is $\_\_\_\_$