{Spam?} Re: Two or three more sequences?? (fwd)

[Richard Guy]

Whoops!

---------- Forwarded message ----------
Date: Tue, 12 Feb 2008 10:06:59 -0800 (PST)
From: Farideh Firoozbakht <mymontain at yahoo.com>
To: Richard Guy <rkg at cpsc.ucalgary.ca>
Subject: {Spam?} Re: Two or three more sequences??

Dear Dr. Guy,

   >  3.  Numbers such that  phi(n) / phi(sigma(n))  =  1/2
> viz.  2, 6, 8, 9, 16, 28, 70, 78

   The sequence  2, 6, 8, 9, 24, 28, 70, 78, ...
   isn't a new sequence.
   Please see A067704 (phi(sigma(n)) = 2*phi(n)).

   We can easily prove that 2^(2^k-1) for k = 1, 2, 3, 4 & 5 are in the
   sequence.

   Best wishes,
   Farideh


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