%I #9 May 01 2021 17:51:44
%S 4,6,8,9,10,12,14,15,16,18,20,21,22,25,26,27,28,30,32,33,34,35,38,39,
%T 44,45,46,49,51,54,55,56,57,58,62,63,65,68,70,77,85,87,91,93,95,99,
%U 104,111,119,121,129,134,143,145,153,158,161,169,189,205,209,215,221,245
%N Starting the iteration of the function Phi[(Sigma[]Phi[])] at these initial values leads to the fixed point 4.
%C Probably this sequence is finite, with 92 terms of which the last is 6241.
%e n=6241: FixedPointList={6241,104,54,32,20,16,22,12,8,10,6,4},end=4.
%t f[x_] := EulerPhi[DivisorSigma[1, x]EulerPhi[x]] Do[s=NestList[f, n, 100]; s1=Part[s, 99]; s2=Part[s, 100]; If[Equal[s1, s2]&&Equal[s1, 4], Print[{n, s1}]], {n, 1, 1000000}]
%t f4[n_]:=FixedPoint[EulerPhi[DivisorSigma[1,#]EulerPhi[#]]&,n,50]==4; Select[Range[250],f4] (* _Harvey P. Dale_, May 01 2021 *)
%Y Cf. A077090A077100.
%K nonn,fini
%O 1,1
%A _Labos Elemer_, Oct 31 2002
%E Definition corrected by _Harvey P. Dale_, May 01 2021
