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%I #7 Jun 22 2023 05:59:29
%S 2,208,388,298,838
%N Least n-untouchable number.
%C 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).
%H Kevin Chum, Richard K. Guy, Michael J. Jacobson Jr. and Anton S. Mosunov, <a href="https://arxiv.org/abs/2110.14136">Numerical and Statistical Analysis of Aliquot Sequences</a>, arXiv:2110.14136 [math.NT], 2021.
%Y Cf. A005114, A152454, A283152, A284147, A284156, A284187.
%K nonn,more
%O 1,1
%A _Jinyuan Wang_, Jun 03 2023