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 A096998 Consider iteration of the function f(x)=sigma(phi(x))=A062402(x). Sequence gives numbers n such that the trajectory of n returns to n. 1
 1, 3, 7, 12, 15, 28, 31, 60, 72, 124, 168, 195, 252, 255, 744, 1240, 1512, 1651, 2418, 2520, 3066, 3844, 4092, 4800, 5080, 5376, 6045, 6138, 6552, 9906, 9920, 10200, 12264, 20440, 30855, 36792, 46228, 58968, 60984, 65535, 67963, 81880, 122640 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS EXAMPLE 96 => 63 => 91 => 195 => 252 => 195 => ..., therefore 195 and 252 are in the sequence. MATHEMATICA 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 *) CROSSREFS Cf. A062402, A096850. Sequence in context: A033015 A225574 A317305 * A317307 A331042 A122981 Adjacent sequences:  A096995 A096996 A096997 * A096999 A097000 A097001 KEYWORD nonn AUTHOR Labos Elemer, Jul 19 2004 EXTENSIONS Edited, corrected and extended by Robert G. Wilson v, Jul 21 2004 STATUS approved

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Last modified May 18 12:26 EDT 2021. Contains 343995 sequences. (Running on oeis4.)