# Greetings from The On-Line Encyclopedia of Integer Sequences! http://oeis.org/

Search: id:a066939
Showing 1-1 of 1

%I A066939 #8 Jun 24 2014 01:08:20
%S A066939 13954,106899,307835,783201,979731,2980255,9266817,18479215,49062925,
%T A066939 109044425,114029313,120914101,185480686,218223299,347941741,
%U A066939 429365395,466423743,492508289,610803875,895938847,993189741,1093958383
%N A066939 Numbers n such that phi(phi(n)) + sigma(sigma(n)) - phi(sigma(n)) - sigma(phi(n)) = phi(n) + sigma(n).
%e A066939 For n = 13954, phi(phi(n)) + sigma(sigma(n)) - phi(sigma(n)) - sigma(phi(n)) = phi(6976) + sigma(20934) - phi(20934) - sigma(6976) = 3456 + 45396 - 6972 - 13970 = 27910 = 6976 + 20934 = phi(n) + sigma(n), so 13954 is in the sequence.
%t A066939 g[x_] := Module[{a, b, c, d, e, f}, a=EulerPhi[x]; b=DivisorSigma[1, x]; c=EulerPhi[a]; d=DivisorSigma[1, b]; e=EulerPhi[b]; f=DivisorSigma[1, a]; a+b==c+d-e-f]; Do[If[g[n]==True, Print[n]], {n, 1, 10^6}]
%Y A066939 Cf. A000010, A000203, A066850, A066945, A066946.
%K A066939 nonn
%O A066939 1,1
%A A066939 _Joseph L. Pe_, Jan 24 2002
%E A066939 Edited by _Dean Hickerson_, Jan 26 2002
%E A066939 a(8)-a(22) from _Donovan Johnson_, Jan 02 2009

# Content is available under The OEIS End-User License Agreement: http://oeis.org/LICENSE