Here, $p , p ^{ n } \in\{1,2, \ldots 50\}$

Now p can take values

$2,3,5,7,11,13,17,23,29,31,37,41,43$ and $47 .$

we can calculate no. of elements in $R$, as

$\left(2,2^{\circ}\right),\left(2,2^{1}\right) \ldots\left(2,2^{5}\right)$

$\left(3,3^{\circ}\right), \ldots\left(3,3^{3}\right)$

$\left(5,5^{\circ}\right), \ldots\left(5,5^{2}\right)$

$\left(7,7^{\circ}\right), \ldots\left(7,7^{2}\right)$

$\left(11,11^{\circ}\right), \ldots\left(11,11^{1}\right)$

And rest for all other two elements each

$n \left( R _{1}\right)=6+4+3+3+(2 \times 10)=36$

Similarly for $R _{2}$

$\left(2,2^{\circ}\right),\left(2,2^{1}\right)$

$\left(47,47^{\circ}\right),\left(47,47^{1}\right)$

$n \left( R _{2}\right)=2 \times 14=28$

$n \left( R _{1}\right)- n \left( R _{2}\right)=36-28=8$