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 A343243 Sociable totient numbers of order 3: numbers k such that s(s(s(k))) = k, but s(k) != k, where s(k) = A092693(k) is the sum of iterated phi function. 0
 20339, 21159, 23883, 35503, 43255, 45375, 365599, 476343, 493047, 746383, 979839, 1097367, 3331135, 3816831, 3972543, 57720703, 68705247, 78376959, 3031407415, 3742563231, 3866214695 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS The numbers k such that s(k) = k are the perfect totient numbers (A082897). a(22) > 2*10^10, if it exists. LINKS Table of n, a(n) for n=1..21. EXAMPLE 20339 is a term since s(20339) = 23883, s(23883) = 21159 and s(21159) = 20339. MATHEMATICA totSum[n_] := Plus @@ FixedPointList[EulerPhi, n] - n - 1; soc3TotQ[n_] := Nest[totSum, n, 3] == n && totSum[n] != n; Select[Range[2, 10^6], soc3TotQ] CROSSREFS Cf. A000010, A082897, A092693, A286233. Sequence in context: A250451 A031825 A234631 * A156408 A045815 A182294 Adjacent sequences: A343240 A343241 A343242 * A343244 A343245 A343246 KEYWORD nonn,more AUTHOR Amiram Eldar, Apr 08 2021 STATUS approved

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Last modified June 1 15:47 EDT 2023. Contains 363074 sequences. (Running on oeis4.)