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%I #8 Mar 12 2023 10:49:20
%S 24,42,69,74,75,82,86,94,115,125,133,155,185,187,203,289,299,323,341,
%T 361,377,437,1681
%N Starting iteration of Phi[]*(Sigma[]-Phi[]) function at these initial values leads to the fixed point 24.
%C Probably this sequence is finite, with 23 terms of which the last is 1681.
%e n=1641: FixedPointList={1681,82,42,24},end=24.
%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 fp24Q[n_]:=FixedPoint[EulerPhi[DivisorSigma[1,#]-EulerPhi[#]]&,n,20]==24; Select[ Range[1700],fp24Q] (* _Harvey P. Dale_, Mar 12 2023 *)
%Y Cf. A077090-A077100.
%K nonn,fini,full
%O 1,1
%A _Labos Elemer_, Oct 31 2002
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