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%I #32 Feb 19 2024 01:56:54
%S 2,4,16,154,256,286,364,804,1066,2146,3382,4550,6106,7700,8176,9268,
%T 11284,12556,12970,16402,19228,19276,20272,25132,26404,27346,29154,
%U 29574,35644,36418,38368,39646,40494,47214,52234,54652,65536,84862
%N Numbers m such that 2*phi(m) = phi(m+1).
%D R. K. Guy, Unsolved Problems Number Theory, Sect. B36.
%H Giovanni Resta, <a href="/A050472/b050472.txt">Table of n, a(n) for n = 1..10000</a> (first 1000 terms from Donovan Johnson)
%F Conjecture : a(n)/n^3 is bounded. Does lim n -> infinity a(n)/n^3 = 2 ? - _Benoit Cloitre_, Aug 07 2002
%F a(n) = A171271(n) - 1. - _Ray Chandler_, May 01 2015
%e phi(256)=128, phi(256+1)=2*128, so 256 is a member of the sequence.
%o (PARI) isok(n) = 2*eulerphi(n) == eulerphi(n+1); \\ _Michel Marcus_, Aug 02 2018
%Y Cf. A000010, A001274, A050473, A171271.
%K nonn
%O 1,1
%A _Jud McCranie_, Dec 24 1999
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