greatest prime factor

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by harshavardhanc » Sun Apr 25, 2010 4:16 am
nisha.menon294 wrote:What is the greatest prime factor of 4^17-2^28

a)2
b)3
c)5
d)7
e)11

OA is D

the question can be re-written as : 2^34 - 2^28

= 2^28 (2^6-1)

= 2^28 * 63

=2^28 * 3^2 * 7

Hence, greatest of 2,3, and 7 will be option D.
Regards,
Harsha