hermann on Wed, 06 Nov 2024 20:32:42 +0100


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Re: Game: find the integers 

On 2024-11-06 20:22, Bill Allombert wrote:

Dear PARI lovers,

A new little game!

Find positive integers n such that

2*eulerphi(n) = n+1

I know 8 solutions, but maybe there are more!

Cheers,
Bill.


The first 5 without thinking from GP below

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V

pi@raspberrypi5:~ $ gp -q
? [n|n<-[0..10000000],2*eulerphi(n)==n+1]
[1, 3, 15, 255, 65535]
? ##
  ***   last result: cpu time 7,203 ms, real time 7,316 ms.
?