

A257348


Repeatedly applying the map x > sigma(x) partitions the natural numbers into a number of disjoint trees; sequence gives (conjectural) list of minimal representatives of these trees.


6



1, 2, 5, 16, 19, 27, 29, 33, 49, 50, 52, 66, 81, 85, 105, 146, 147, 163, 170, 189, 197, 199, 218, 226, 243, 262, 303, 315, 343, 424, 430, 438, 453, 461, 463, 469, 472, 484, 489, 513, 530, 550, 584, 677, 722, 746, 786, 787, 804, 813, 821, 831, 842, 859, 867, 876, 892, 903, 914, 916, 937, 977, 982, 988, 990, 1029
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OFFSET

1,2


COMMENTS

Very little is known for certain. Even the trajectories of 2 (A007497) and 5 (A051572) under repeated application of the map x > sigma(x) (cf. A000203) are only conjectured to be disjoint.


REFERENCES

Kerry Mitchell, Posting to Math Fun Mailing List, Apr 30 2015


LINKS

Hans Havermann, Table of n, a(n) for n = 1..1000
G. L. Cohen and H. J. J. te Riele, Iterating the sumofdivisors function, Experimental Mathematics, 5 (1996), pp. 91100. See Eq. (4.2).


CROSSREFS

Cf. A000203 (sigma), A007497 (trajectory of 2), A051572 (trajectory of 5), A257349 (trajectory of 16).
Cf. A216200 (number of disjoint trees).
Sequence in context: A286382 A127580 A098048 * A101847 A251600 A117557
Adjacent sequences: A257345 A257346 A257347 * A257349 A257350 A257351


KEYWORD

nonn,hard


AUTHOR

N. J. A. Sloane, May 01 2015, following a suggestion from Kerry Mitchell.


EXTENSIONS

More terms from Hans Havermann, May 02 2015


STATUS

approved



