# Thread: Is it a prime number ??

1. ## Is it a prime number ??

Is $\displaystyle 2^{30}-1$ prime number ? explain ...

2. Originally Posted by razemsoft21
Is $\displaystyle 2^{30}-1$ prime number ? explain ...
Hint: $\displaystyle 2^{30} - 1 = (2^{15})^2 - 1^2 = (2^{15} + 1)(2^{15} - 1)$

3. Originally Posted by Jhevon
Hint: $\displaystyle 2^{30} - 1 = (2^{15})^2 - 1^2 = (2^{15} + 1)(2^{15} - 1)$
I know that:
$\displaystyle 2^{30} - 1 = (2^{15})^2 - 1^2 = (2^{15} + 1)(2^{15} - 1)$
and
$\displaystyle 2^{30} - 1 = (2^{10})^3 - 1^3 = (2^{10} - 1)(2^{20} + 2^{10} + 1)$

sorry, how can I know that this is prime or not ?

4. Originally Posted by razemsoft21
I know that:
$\displaystyle 2^{30} - 1 = (2^{15})^2 - 1^2 = (2^{15} + 1)(2^{15} - 1)$
and
$\displaystyle 2^{30} - 1 = (2^{10})^3 - 1^3 = (2^{10} - 1)(2^{20} + 2^{10} + 1)$

sorry, how can I know that this is prime or not ?
what's a prime number?answer this question to your self.
If x is a natural number and y is another natural number other than 1

Can xy be a prime number ??

5. Originally Posted by ADARSH
what's a prime number?answer this question to your self.
If x is a natural number and y is another natural number other than 1

Can xy be a prime number ??
since we can factorize it $\displaystyle \Rightarrow$ it is not prime

Thanks a lot.