Qn about CS1231SHow to prove that if 2^n+1 is a prime, then n is a power of 2?

you are wrongpls look at the question again. saying if 2^p+1 is a prime, then p is the power of 2. You just showed that the reverse statement is wrong. The original statement is correct.

come inif n is not a power of 2, then there exists an odd prime dividing n, say p. then, n=pq. then, 2^n+1=2^pq+1=(2^q+1)(2^(p-1)q-2^(p-2)q+...+2^2q-2^q+1) and p is odd, LHS=RHS. QED.