This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A259178 #20 Sep 08 2022 08:46:13 %S A259178 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 A259178 33,34,35,37,38,39,41,43,44,46,47,48,49,51,52,53,56,57,58,59,61,62,64, %U A259178 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 A259178 Numbers k such that (4^k - 1)/3 is squarefree. %H A259178 Amiram Eldar, <a href="/A259178/b259178.txt">Table of n, a(n) for n = 1..467</a> %t A259178 Select[Range[0, 120], SquareFreeQ[((4^# - 1) / 3)] &] (* _Vincenzo Librandi_, Aug 03 2015 *) %o A259178 (Magma) [n: n in [1..115] | IsSquarefree((4^n-1) div 3)]; // _Vincenzo Librandi_, Aug 03 2015 %o A259178 (PARI) isok(k) = issquarefree((4^k-1)/3); \\ _Michel Marcus_, Feb 25 2021 %Y A259178 Complement of A260042. %Y A259178 Cf. A002450, A005117, A008966. %K A259178 nonn %O A259178 1,2 %A A259178 _Omar E. Pol_, Aug 02 2015