Greatest prime factor

[bstalling]

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

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

Clearly, I'm missing something. Why is it not A

OA - D

[gaggleofgirls]

Because 2^34 - s^28 does not = 2^6

2^34/2^28 = 2^6

So, we need to figure out something useful to do with 2^34 - 2^28

Factor out 2^28 and you get:

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

2^28 has a whole bunh of 2s as its factors, but 63 is 7 * 3 * 3,

So the greatest prime factor of 2^28(63) = 7.

Answer = D.

-Carrie