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Quasiperfect cototient numbers: numbers k such that the sum of the iterated cototient function of k is equal to k+1.
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%I #4 Mar 07 2020 20:19:18

%S 6,14,62,254,16382,78585,87465,262142,1048574

%N Quasiperfect cototient numbers: numbers k such that the sum of the iterated cototient function of k is equal to k+1.

%C If m is in A050475 then 2^m - 2 is a term.

%C 3*10^8 < a(10) <= 4294967292.

%H Wikipedia, <a href="https://en.wikipedia.org/wiki/Perfect_totient_number">Perfect totient number</a>.

%H Wikipedia, <a href="https://en.wikipedia.org/wiki/Quasiperfect_number">Quasiperfect number</a>.

%e 6 is a term since A051953(6) = 4, A051953(4) = 2, A051953(2) = 1, and 4 + 2 + 1 = 7 = 6 + 1.

%t cot[n_] := n - EulerPhi[n]; s[n_] := Plus @@ FixedPointList[cot, n]; Select[Range[10^5], s[#] == 2*# + 1 &]

%Y Cf. A050475, A051953, A082897, A286067, A330273.

%K nonn,more

%O 1,1

%A _Amiram Eldar_, Mar 07 2020