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%I #9 Sep 09 2023 22:28:11
%S 1,3,7,12,15,28,31,60,72,124,168,195,252,255,744,1240,1512,1651,2418,
%T 2520,3066,3844,4092,4800,5080,5376,6045,6138,6552,9906,9920,10200,
%U 12264,20440,30855,36792,46228,58968,60984,65535,67963,81880,122640
%N Consider iteration of the function f(x) = sigma(phi(x)) = A062402(x). Sequence lists the numbers k such that the trajectory of k returns to k.
%e 96 => 63 => 91 => 195 => 252 => 195 => ..., therefore 195 and 252 are in the sequence.
%t a = {}; f[n_] := DivisorSigma[1, EulerPhi[ n]]; Do[ AppendTo[ a, NestWhileList[f, n, UnsameQ, All][[ -1]]]; a = Union[a], {n, 10^6}]; Take[ a, 43] (* _Robert G. Wilson v_, Jul 21 2004 *)
%Y Cf. A062402, A096850.
%K nonn
%O 1,2
%A _Labos Elemer_, Jul 19 2004
%E Edited, corrected and extended by _Robert G. Wilson v_, Jul 21 2004
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