A363461 Least n-untouchable number.

2, 208, 388, 298, 838

Offset

1,1

Comments

Let s^m(k) denote the m-th iterate of s(k) = sigma(k) - k. n-untouchable numbers are the numbers that lie in the image of s^(n-1)(k), but not in the image of s^n(k).

Links

Table of n, a(n) for n=1..5.

Kevin Chum, Richard K. Guy, Michael J. Jacobson Jr. and Anton S. Mosunov, Numerical and Statistical Analysis of Aliquot Sequences, arXiv:2110.14136 [math.NT], 2021.

Crossrefs

Cf. A005114, A152454, A283152, A284147, A284156, A284187.

Sequence in context: A375842 A238819 A110899 * A281126 A220940 A012600

Adjacent sequences: A363458 A363459 A363460 * A363462 A363463 A363464

Keyword

nonn,more

Author

Jinyuan Wang, Jun 03 2023

Status

approved