The correct option is D the HCF of N1 and N2 is 33
Given that N1=255+1 and N2=165=3×5×11
22n+1+1 is divisible by 3. So, 255 is divisible by 3.
255 ends with 8. So, 255+1 ends with 9 and thus not divisible by 5.
255mod(11)=(32)11mod11=10
⇒255=11k+10⇒N1=11k+11,
so, N1 is divisible by 11
So, the HCF of N1 and N2 is 33.