What is the greatest prime factor of

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Lookingfor700GMAT
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Topic: What is the greatest prime factor of

Wed Mar 10, 2010 10:21 am

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4^-2^28

2
3
5
7
11

Please can you explain how this is solved.

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Lookingfor700GMAT
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Wed Mar 10, 2010 10:48 am

To be clear the stimulus is 4^17-2^28

osirus0830
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Wed Mar 10, 2010 11:05 am

rewrite 4^17 as (2^2)^17 This equals 2^34 Now you have to factor 2^34 - 2^28 this equals 2^28 (2^6 - 1) this equals 2^28 (64-1) This equals 2^28 (63) 63 broken into prime factors is 3^2 * 7 Therefore, the greatest prime factor is 7 _________________ http://www.beatthegmat.com/the-retake-osirus-blog-t51414.html

Lookingfor700GMAT
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Wed Mar 10, 2010 11:48 am

Awesome stuff. Thanks!

Lookingfor700GMAT
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Wed Mar 10, 2010 12:07 pm

Actually can you explain these steps again please rewrite 4^17 as (2^2)^17 This equals 2^34 Now you have to factor 2^34 - 2^28 this equals 2^28 (2^6 - 1)