PRIME NUMBER is the relation given always true or is it false, $2^n-1$

Question

If n is a prime no. Is it necessary that $2^n - 1$ is also a prime no. I know that the converse is true, but i want to know about this statement. If it's wrong plz. Give an eg. If its right plz. Prove it.

False probably for most primes $n$. Smallest counterexample is $n=11$. — André Nicolas, Sep 08 '15 at 06:35
Plz guys I am not that good in Maths plz. Be soft. Thnx for your answers — Display name, Sep 08 '15 at 06:38

score 1 · Answer 1 · answered Sep 08 '15 at 06:35

1

Check if $2^{11}-1$ is prime. It's merely the fifth candidate ...

answered Sep 08 '15 at 06:35

Hagen von Eitzen

374,180

PRIME NUMBER is the relation given always true or is it false, $2^n-1$

1 Answers1