A220160 - OEIS

%I #10 Feb 04 2015 19:42:58

%S 194,3530,9338,27230,46794,78182,90194,112994,135014,437184,849404,

%T 935220,1078580,1283600,1986974,2209584,2341184,2411174,2689694,

%U 2744144,3619070,3712544,4738184,5132984,6596120,7829030,8184714,12176108,12292004,13342958,26400842

%N Numbers n for which phi(n) = phi(n-1) - phi(n+1).

%H Donovan Johnson, <a href="/A220160/b220160.txt">Table of n, a(n) for n = 1..100</a>

%e phi(3529) - phi(3531) = 3528 - 2120 = 1408 = phi(3530).

%t Select[Range[10^6], EulerPhi[#] == EulerPhi[# - 1] - EulerPhi[# + 1] &]

%t With[{ep=EulerPhi[Range[27500000]]},Flatten[Position[Partition[ ep,3,1], _?(#[[1]]- #[[3]]==#[[2]]&),{1},Heads->False]]]+1 (* _Harvey P. Dale_, Feb 04 2015 *)

%Y Cf. A000010, A076529.

%K nonn

%O 1,1

%A _Carl Najafi_, Dec 06 2012