This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A343243 #5 Apr 08 2021 22:11:30 %S A343243 20339,21159,23883,35503,43255,45375,365599,476343,493047,746383, %T A343243 979839,1097367,3331135,3816831,3972543,57720703,68705247,78376959, %U A343243 3031407415,3742563231,3866214695 %N 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. %C A343243 The numbers k such that s(k) = k are the perfect totient numbers (A082897). %C A343243 a(22) > 2*10^10, if it exists. %e A343243 20339 is a term since s(20339) = 23883, s(23883) = 21159 and s(21159) = 20339. %t A343243 totSum[n_] := Plus @@ FixedPointList[EulerPhi, n] - n - 1; soc3TotQ[n_] := Nest[totSum, n, 3] == n && totSum[n] != n; Select[Range[2, 10^6], soc3TotQ] %Y A343243 Cf. A000010, A082897, A092693, A286233. %K A343243 nonn,more %O A343243 1,1 %A A343243 _Amiram Eldar_, Apr 08 2021