greatest prime factor

BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

DeeeJaaayyy: Newbie | Next Rank: 10 Posts; Posts: 1; Joined: Thu Oct 01, 2009 6:10 pm

by DeeeJaaayyy » Mon Oct 05, 2009 4:48 pm

What is the greatest prime factor of 4^17-2^28?

A) 2
B) 3
C) 5
D) 7
E) 11

Can i get some help on how to solve this?

Source: Beat The GMAT — Problem Solving | Mon Oct 05, 2009 4:48 pm

umaa: Legendary Member; Posts: 727; Joined: Sun Jun 08, 2008 9:32 pm; Thanked: 8 times; Followed by:1 members

by umaa » Mon Oct 05, 2009 5:05 pm

DeeeJaaayyy wrote:What is the greatest prime factor of 4^17-2^28?

A) 2
B) 3
C) 5
D) 7
E) 11

Can i get some help on how to solve this?

IMO D.

4^17 = 2^34

2^34 - 2^28 = 2^28(2^6 - 1) = 2^28 (63).

The factors are, 1, 2, 7, 3.

The greatest prime number is 7.

What we think, we become

• Page 1 of 1