Question

Thanks guys -
Find the greatest prime factor of 2^20-1

(I got 41, could someone tell me if that is correct and how they obtained their solution?)

Answer 1

2^(20-1)?

Answer 2

(2^20)-2

Answer 3

Whoops, (2^20)-1

Answer 4

so you are try to find the largest prime p such that \[2^{20}\equiv 1(mod p)\]

Answer 5

Yes. I totally forgot how to use modulus, but yes, I believe that is it.

Answer 6

yeah my number theory is a bit rusty, I would need to look up some theorems as well...

Answer 7

Oh darn. =] Anyone care to help?