The OEIS is supported by the many generous donors to the OEIS Foundation.
%I #28 Nov 19 2022 14:51:08
%S 5,10,14,20,25,50,80,154,200,434,520,610,815,1205,1345,2680,3200,3560,
%T 4669,7330,9290,10130,11705,17630,24410,25090,33385,34205,39754,39785,
%U 40870,48470,55979,59090,73165,75470,78035,95990,107680,115685,120230
%N Numbers k such that (phi(k-2) + phi(k+2))/2 = phi(k); 2-phi/balanced numbers.
%H Donovan Johnson, <a href="/A099633/b099633.txt">Table of n, a(n) for n = 1..499</a>
%e k=154, phi(152)=72, phi(156)=48, phi(154)=60.
%t Flatten[Position[Partition[EulerPhi[Range[121000]],5,1],_?((#[[1]]+ #[[5]]) /2 == #[[3]]&),{1},Heads->False]]+2 (* _Harvey P. Dale_, Jan 20 2015 *)
%o (PARI) isok(k) = (k>2) && (eulerphi(k-2)+eulerphi(k+2) == 2*eulerphi(k)); \\ _Michel Marcus_, Nov 18 2022
%Y Cf. A066167, A000010, A099631, A099632.
%K nonn
%O 1,1
%A _Labos Elemer_, Oct 27 2004
%E Incorrect term 2 removed by _Michel Marcus_, Nov 19 2022