Thinking about Numbers
Review question

When is $4^n-1$ prime?
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Ref: R5927
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Suggestion

For how many positive integers \(n\) is \(4^n-1\) a prime number?

Is it possible to factorise \(4^n-1\)?

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UKMT Senior Mathematical Challenge, 2013, Q15

Question reproduced by kind permission of the United Kingdom Mathematics Trust. The question remains Copyright UKMT, All rights reserved.

 Last updated 12-Feb-16
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