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by bkobilov » Thu Sep 30, 2010 8:29 am
Seems to be easy question, but cant solve it

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

2
3
5
7
11
OA: D
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by neerajkumar1_1 » Thu Sep 30, 2010 8:34 am
bkobilov wrote:Seems to be easy question, but cant solve it

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

2
3
5
7
11
OA: D
this is how i will solve it...

4^17-2^28 = 2^34 - 2^28
take 2^28 common, we get

=2^28(2^6-1)
=2^28(63)= 2^28 * 7 * 3^2

so the prime factors are 2,3, and 7

highest is 7

IMO: D
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by narik11 » Thu Sep 30, 2010 8:37 am
bkobilov wrote:Seems to be easy question, but cant solve it

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

2
3
5
7
11
OA: D
4^17-2^28=> 2^34-2^28
2^28(2^6-1)
2^28(63)=> 2^28*3^2*7

greatest prime factor is 7
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