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%I #20 Dec 09 2022 07:07:40
%S 1,3,5,9,15,21,35,39,45,99,135,231,255,855,1035,1295,1539,1599,2015,
%T 4335,6525,9177,14399,16095,30495,55385,61131,62799,65535,72579,77615,
%U 110175,152649,179295,244965,299649,603459,619695,686735,1876725,2841915,3058209
%N Numbers k such that phi(k) = phi(k+2) - phi(k+1).
%H Donovan Johnson and Giovanni Resta, <a href="/A229552/b229552.txt">Table of n, a(n) for n = 1..324</a> (terms < 10^13, first 100 terms from Donovan Johnson)
%F a(n) = A065557(n) - 2. - _Amiram Eldar_, Dec 09 2022
%t Select[Range[10^6], EulerPhi[#] == EulerPhi[# + 2] - EulerPhi[# + 1] &]
%t Position[Partition[EulerPhi[Range[31*10^5]],3,1],_?(#[[3]]-#[[2]] == #[[1]]&),1,Heads->False]//Flatten (* _Harvey P. Dale_, Nov 29 2017 *)
%Y Cf. A092404, A197112, A057000, A000010, A065557.
%K nonn
%O 1,2
%A _Vincenzo Librandi_, Sep 27 2013
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