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%I #20 Aug 19 2018 12:47:22
%S 6,8,26,78,218,306,3666,4646,5066,8816,12206,12546,19878,20436,24236,
%T 29546,37736,47996,60116,72086,73026,77046,87476,121146,126056,129246,
%U 149756,190268,234636,247856,273296,275724,419366,531236,553476,621726
%N Numbers n such that phi(n) = phi(n-1) - phi(n-2).
%C Question: Are all terms of this sequence even? (Compare A065557, whose terms could be all odd and squarefree.)
%H Harry J. Smith and Jud McCranie, <a href="/A066231/b066231.txt">Table of n, a(n) for n = 1..494</a> (first 117 terms from Harry J. Smith)
%e phi(8) = 4 = 6-2 = phi(7) - phi(6).
%t Flatten[Position[Partition[EulerPhi[Range[630000]],3,1],_?(#[[3]] == #[[2]]- #[[1]]&),1,Heads->False]]+2 (* _Harvey P. Dale_, Aug 19 2018 *)
%o (PARI) n=0; for (m=3, 10^9, if (eulerphi(m) == eulerphi(m - 1) - eulerphi(m - 2), write("b066231.txt", n++, " ", m); if (n==117, return)) ) \\ _Harry J. Smith_, Feb 06 2010
%Y Cf. A066232, A067701.
%K nonn
%O 1,1
%A _Joseph L. Pe_, Dec 18 2001
%E a(24)-a(36) from _Harry J. Smith_, Feb 06 2010