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Least k such that phi(k) = phi(n).
7

%I #20 Nov 11 2022 11:36:13

%S 1,1,3,3,5,3,7,5,7,5,11,5,13,7,15,15,17,7,19,15,13,11,23,15,25,13,19,

%T 13,29,15,31,17,25,17,35,13,37,19,35,17,41,13,43,25,35,23,47,17,43,25,

%U 51,35,53,19,41,35,37,29,59,17,61,31,37,51,65,25,67,51,69,35,71,35,73

%N Least k such that phi(k) = phi(n).

%C From _Jianing Song_, Nov 11 2022: (Start)

%C The first even term is a(33817088) = 16842752 (see A002181 and A143510).

%C Conjecture: a(n) is always odd for odd n. (End)

%H Antti Karttunen, <a href="/A015126/b015126.txt">Table of n, a(n) for n = 1..10000</a>

%o (PARI) a(n) = {my(en = eulerphi(n)); k = 1; while (eulerphi(k) != en, k++); return (k);} \\ _Michel Marcus_, Jun 17 2013

%Y Cf. A000010, A028476, A066412, A066659.

%Y Cf. A002181, A143510.

%K nonn,look

%O 1,3

%A _Vladeta Jovovic_, Jan 12 2002