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Numbers n that have a record maximum in their unitary aliquot sequence.
1

%I #12 Jul 24 2017 12:36:26

%S 30,66,102,138,174,210,318,1110,1398,6870,19866,89610,291450,705990

%N Numbers n that have a record maximum in their unitary aliquot sequence.

%C Maximum term in the aliquot sequence of n is considered only if it is larger than n.

%C The record values are in A290146.

%C te Riele found the unitary aliquot sequences of all numbers < 10^5, except for 89610. He terminated the calculation of the unitary aliquot sequence of 89610 at the 541st iteration, at 114601234388928504726, while the maximum, 645856907610421353834, is reached at the 569th iteration.

%D H. J. J. te Riele, Further Results On Unitary Aliquot Sequences. NW 2/73, Mathematisch Centrum, 1973, Amsterdam.

%e The unitary aliquot sequence of 174 is: 174, 186, 198, 162, 84, 76, 24, 12, 8, 1. Its maximum is 198 which larger than the maxima of all the aliquot sequences of the numbers below 174.

%t usigma[n_] := If[n == 1, 1, Times @@ (1 + Power @@@ FactorInteger[n])];

%t g[n_] := If[n > 0, usigma[n] - n, 0]; f[n_] := NestWhileList[g, n, UnsameQ, All]; a = -1; rec = {}; Do[b = Length[f[n]] - 2;

%t If[b > a, a = b; AppendTo[rec, n]], {n, 10^6}] ; rec (* after _Giovanni Resta_ at A034448 & _Robert G. Wilson v_ at A098009 *)

%Y Cf. A098008, A098009, A098010, A290146.

%K nonn,more

%O 1,1

%A _Amiram Eldar_, Jul 21 2017