What is the greatest prime factor of $3^6 - 1?$ - The Beat The GMAT Forum

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Re: What is the greatest prime factor of $3^6 - 1?$

by Scott@TargetTestPrep » Tue Nov 17, 2020 8:40 am

Gmat_mission wrote: ↑
Tue Nov 10, 2020 7:53 am
What is the greatest prime factor of $3^6 - 1?$

A. 2
B. 3
C. 7
D. 13
E. 17

Answer: D

Solution:

Since 3^6 - 1 = (3^3 + 1)(3^3 - 1) = 28 x 26 = 2^2 x 7 x 2 x 13, we see that its largest prime factor is 13.

Answer: D

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