I have mistaken the vertical bar as a divisor. It took me a while before I realized that it's
I did not know what meant until I read up on the Mersenne prime and Euclid's proof.
My book has devoted only one chapter on number theory, and I was expected to this proof without much instruction. I am glad you showed the proof.
I am an engineering student. I learn pure math on my own. Could you recommend me a book on number theory that's easy for my independent study.