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%I #13 Feb 24 2024 01:04:58
%S 0,4,24,8064,34944,35520,38880,69480,268560,420096,1054944,2946560,
%T 3054080,5660160,6621120,9768960,10264320,25885760,29062656,33933312,
%U 36484992,38707200,78532608,163418112,260601600,458987520,4044349440
%N Fixed points of iteration in A077091.
%C When iteration of f[]=Phi[Sigma[]-Phi[]] is started at various initial values, not ending in cycles and converging, it ends at these fixed points.
%C a(28) <= 11435212800. a(29) <= 15083274240. a(30) <= 90215424000. [From _Donovan Johnson_, Dec 14 2009]
%e n=30: FixedPointList={30,32,46,20,16,22,12,8,10,6,4},end=4; n=94: FixedPointList={94,42,24},end=24. n=41708: FixedPointList={41708,26064,32352,21216,15232,8064},end=8064; n=12100: FixedPointList={12100,24000,34944},end=34944.
%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]&&!PrimeQ[n], Print[{n, s1}]], {n, 1, 1000}]
%Y Cf. A077090-A077100.
%K nonn
%O 1,2
%A _Labos Elemer_, Oct 31 2002
%E a(9) corrected and a(11)-a(27) from _Donovan Johnson_, Dec 14 2009
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