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A292766 Numbers n whose trajectory under iteration of the map k -> (sigma(k)+phi(k))/2 consists only of integers and is unbounded, excluding numbers n whose trajectory merges with the trajectory of a smaller number. 2
270, 440, 496, 702, 737, 813, 828, 897, 905, 1027, 1066, 1099, 1240, 1241, 1260, 1331, 1353, 1368, 1371, 1422, 1507, 1537, 1754, 1760, 1834, 1848, 2002, 2016, 2282 (list; graph; refs; listen; history; text; internal format)



These are the "seeds" in A291790, that is, every number which blows up under iteration of the map k -> (sigma(k)+phi(k))/2 belongs to one of these trajectories. AT PRESENT ALL TERMS ARE CONJECTURAL.

The trajectories of these numbers are pairwise disjoint for the first 400 steps.

This is unsatisfactory because it is possible that, at some later step, these trajectories may merge, reach a prime (a fixed point), or reach a fraction (and die). However, this seems unlikely on probabilistic grounds - see the remarks of Andrew R. Booker in A292108.

Normally such a sequence would not be included in the OEIS, but exceptions have been made for this and A291790 because a number of people have worked on them, and also in the hope that this will encourage resolution of some of the open questions.

Needs a b-file.


Table of n, a(n) for n=1..29.

Sean A. Irvine, Showing how the initial portions of some of these trajectories merge


Cf. A291790, A292108.

Sequence in context: A291790 A025394 A291789 * A180151 A278130 A206088

Adjacent sequences:  A292763 A292764 A292765 * A292767 A292768 A292769




N. J. A. Sloane, Sep 27 2017, based on emails from Sean A. Irvine, Sep 14 2017, who computed a(1)-a(9), and Hans Havermann, same date, who computed a(10)-a(29). Hugo Pfoertner also computed many of these terms.



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Last modified March 2 12:26 EST 2021. Contains 341750 sequences. (Running on oeis4.)