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%I #28 Sep 08 2022 08:45:46
%S 314,524,734,824,944,974,1154,1364,1574,1754,1784,1814,1994,2144,2414,
%T 2474,2624,2804,3044,3134,3254,3314,3464,3704,3884,4094,4124,4304,
%U 4388,4514,4724,4874,4934,5114,5144,5354,5444,5564,5774,5864
%N Even numbers n for which phi(n) > phi(n+1).
%C If n is even then for obvious reasons phi(n) will usually be less than or equal to phi(n+1). These are the first few exceptions.
%C Observation based upon calculation: More than 95% of the terms of this sequence have the final digit of 4 for n <= 10^7.. - _Harvey P. Dale_, Jul 24 2012
%H G. C. Greubel, <a href="/A161963/b161963.txt">Table of n, a(n) for n = 1..5000</a> (terms 1..1000 from T. D. Noe)
%F a(n) = 2 * A001837(n) (follows from the definition). - _Chris Boyd_, Mar 15 2014
%e 314 is in the list because phi(314)=156 and phi(315)=144.
%t Select[2*Range[3000],EulerPhi[#]>EulerPhi[#+1]&] (* _Harvey P. Dale_, Jul 24 2012 *)
%o (PARI) for(n=1, 6000, if(Mod(n,2)==0 && eulerphi(n) > eulerphi(n+1), print1(n", "))) \\ _G. C. Greubel_, Feb 27 2019
%o (Magma) [n: n in [1..6000] | (n mod 2 eq 0) and (EulerPhi(n) gt EulerPhi(n+1))]; // _G. C. Greubel_, Feb 27 2019
%o (Sage) [n for n in (1..6000) if mod(n,2)==0 and euler_phi(n) > euler_phi(n+1)] # _G. C. Greubel_, Feb 27 2019
%Y Cf. A001837, A161962.
%K easy,nonn
%O 1,1
%A David Angell (angell(AT)maths.unsw.edu.au), Jun 22 2009
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