I would argue that if n is a perfect square i.e $\displaystyle n=a^2$ then $\displaystyle n-1 = a^2-1 $ , now $\displaystyle a^2-1$ can be factored into $\displaystyle (a-1)(a+1)$ and in turn so can n-1 so it cannot be prime.
Buddy,
I did not understand that. Is'nt prefect number is different than perfect squre? Please help me solve the question.
First of all, I doubt that I am your ‘buddy’. I have no idea who you could be.
From this reply it is clear that you don’t even understand your own question.