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%I #8 Jul 30 2020 01:57:34
%S 1,2,3,4,6,7,8,9,11,12,14,18,21,22,23,24,28,31,33,36,42,43,44,46,47,
%T 49,56,59,62,63,66,67,69,71,72,77,79,83,84,86,88,92,93,94,98,99,103,
%U 107,118,121,124,126,129,131,132,134,138,139,141,142,147,154,158,161
%N Numbers k such that lambda(k) is squarefree, where lambda is the Carmichael lambda function (A002322).
%H Amiram Eldar, <a href="/A336654/b336654.txt">Table of n, a(n) for n = 1..10000</a>
%H Imre Kátai, <a href="https://eudml.org/doc/227184">Square-free values of the Carmichael function</a>, Mathematica Pannonica, Vol. 16, No. 2 (2005), pp. 199-203.
%H Francesco Pappalardi, Filip Saidak and Igor E. Shparlinski, <a href="https://doi.org/10.1016/S0022-314X(03)00110-0">Square-free values of the Carmichael function</a>, Journal of Number Theory, Vol. 103, No. 1 (2003), pp. 122-131.
%F The number of terms not exceeding x is (k + o(1)) * x/(log(x)^(1-a)), where a = 0.373955... is Artin's constant (A005596), and k = 0.80328... is another constant (Pappalardi et al., 2003).
%e 6 is a term since lambda(6) = 2 is squarefree.
%t Select[Range[160], SquareFreeQ[CarmichaelLambda[#]] &]
%Y Cf. A002322, A005117, A005596, A049149, A336655, A336656.
%K nonn
%O 1,2
%A _Amiram Eldar_, Jul 28 2020
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