%I #12 Oct 15 2013 22:32:22
%S 75973,301513,2053393,3404053,4022573,5399123,6461473,8395613,9848813,
%T 11804173,14124133,15680573,17173333,20705533,23609083,28988353,
%U 30290563,32845633,35025943,36791813,39630803,42598663,43605943,44116333,53795083,54396533,54563693
%N Numbers n such that phi(n) = phi(3n+1).
%C Is it accidental that most terms have form 10k+3?
%H Donovan Johnson, <a href="/A091294/b091294.txt">Table of n, a(n) for n = 1..100</a>
%t Do[If[Equal[EulerPhi[n], EulerPhi[3*n+1]], Print[n]], {n, 1, 100000000}]
%o (PARI) is(n)=my(t=eulerphi(3*n+1)); t<n && t==eulerphi(n) \\ _Charles R Greathouse IV_, May 19 2013
%Y Cf. A000010, A092272.
%K nonn
%O 1,1
%A _Labos Elemer_, Feb 19 2004
%E a(20)-a(27) from _Donovan Johnson_, Jul 27 2011