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%I #20 Sep 08 2022 08:46:13
%S 1,2,3,4,5,6,7,8,11,12,13,14,15,16,17,19,22,23,24,25,26,28,29,31,32,
%T 33,34,35,37,38,39,41,43,44,46,47,48,49,51,52,53,56,57,58,59,61,62,64,
%U 65,66,67,69,71,73,74,75,76,77,79,82,83,85,86,87,88,89,91,92,93,94,95,96,97,98,101,102,103,104,106,107,109,111
%N Numbers k such that (4^k - 1)/3 is squarefree.
%H Amiram Eldar, <a href="/A259178/b259178.txt">Table of n, a(n) for n = 1..467</a>
%t Select[Range[0, 120], SquareFreeQ[((4^# - 1) / 3)] &] (* _Vincenzo Librandi_, Aug 03 2015 *)
%o (Magma) [n: n in [1..115] | IsSquarefree((4^n-1) div 3)]; // _Vincenzo Librandi_, Aug 03 2015
%o (PARI) isok(k) = issquarefree((4^k-1)/3); \\ _Michel Marcus_, Feb 25 2021
%Y Complement of A260042.
%Y Cf. A002450, A005117, A008966.
%K nonn
%O 1,2
%A _Omar E. Pol_, Aug 02 2015