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Numbers k such that k and k+2 are consecutive cubefree numbers.
3

%I #8 Nov 12 2021 04:36:10

%S 7,15,23,26,31,39,47,53,55,63,71,87,95,103,107,111,119,124,127,143,

%T 151,159,161,167,175,183,188,191,199,207,215,223,231,239,242,247,249,

%U 255,263,269,271,279,287,303,311,319,323,327,335,359,367,377,383,391,399

%N Numbers k such that k and k+2 are consecutive cubefree numbers.

%C The asymptotic density of this sequence is 0.142325864924778... (Mossinghoff et al., 2021).

%H Amiram Eldar, <a href="/A349233/b349233.txt">Table of n, a(n) for n = 1..10000</a>

%H Michael J. Mossinghoff, Tomás Oliveira e Silva, and Tim Trudgian, <a href="https://doi.org/10.1090/mcom/3581">The distribution of k-free numbers</a>, Mathematics of Computation, Vol. 90, No. 328 (2021), pp. 907-929; <a href="https://arxiv.org/abs/1912.04972">arXiv preprint</a>, arXiv:1912.04972 [math.NT], 2019-2020.

%e 7 is a term since 7 and 7 + 2 = 9 = 3^2 are cubefree, and 7 + 1 = 8 = 2^3 is not.

%t cubeFreeQ[n_] := AllTrue[FactorInteger[n][[;; , 2]], # < 3 &]; Select[Range[400], Boole[cubeFreeQ /@ (# + {0, 1, 2})] == {1, 0, 1} &]

%Y Cf. A004709, A046099, A340152, A349234, A349235.

%K nonn

%O 1,1

%A _Amiram Eldar_, Nov 11 2021