GMAT Prep (Greatest Prime Factor) Pract2

[dferm]

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

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

Please Help...

Thanks...

[aatech]

4^17 = (2^2)^17 = 2^34 = (2^28)*(2^6)

eq becomes (2^28)[(2^6)-1] = (2^28)*63 = (2^28)*9*7

Ans D. What's the OA

[dferm]

Don't understand your logic...

[aatech]

Which part??? Did you get little bit or nothing.. I will try to explain in a diff way...

[dferm]

Nothing...