Let $R_1$ and $R_2$ be relations on the set $\{1,2, \ldots \ldots, 50\}$ such that $\mathrm{R}_1=\left\{\left(\mathrm{p}, \mathrm{p}^{\mathrm{n}}\right): \mathrm{p}\right.$ is a prime and $\mathrm{n} \geq 0$ is an integer $\}$ and $\mathrm{R}_2=\left\{\left(\mathrm{p}, \mathrm{p}^{\mathrm{n}}\right): \mathrm{p}\right.$ is a prime and $\mathrm{n}=0$ or 1$\}$. Then, the number of elements in $\mathrm{R}_1-\mathrm{R}_2$ is $\_\_\_\_$