greatest prime factor

[gayu]

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

A)2 B)3 C)5 D)7 E)4

[manpsingh87]

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

A)2 B)3 C)5 D)7 E)4

4^17=2^34;
therefore; 2^34-2^28;
2^28(2^6-1);
2^28*63;
now 63 is divisible by 7; hence greatest prime factor is 7..!!!!