Let R₁ and R₂ be relations on the set {1,2,.....50} such that 
 $\begin{array}{l}{R}_1=\{(p,p^n):pisaprimeandn\ge 0isan\mathrm{int}eger\}and\\ R_2=\left\{\left(p,p^n\right):pisaprimeandn=0or1\right\}\end{array}$

Then, the number of elements in R₁-R₂  is___________.

Given a set {1,2,....50}
Possible choices of P are 
2,3,5,7,11,13,17,23,29,31,37,41,43 and 47. So , we can calcualte no, of elemetns in R1 as

Every number of pⁿ

 should lie in the given set 

Total number of relations R1 are  38

$$\begin{gathered} similarly relation R2 \\ \left(2,2^0\right),\left(2,2^1\right)\dots ..\left(47,{47}^0\right),\left(47,{47}^1\right) \end{gathered}$$

Total number of relations R2 =15*2=30

required difference = n(R!)-n(R2)=38-30=8