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 A119356 #23 Sep 24 2024 09:24:26
%S A119356 1,2,3,4,5,6,9,10,11,14,17,18,19,20,21,22,28,29,30,33,34,35,36,38,41,
%T A119356 42,43,44,45,46,51,52,57,58,59,61,65,66,68,69,70,76,77,78,82,83,85,86,
%U A119356 89,90,91,92,93,101,102,105,106,109,110,113,114,115,116,117,118,123,126
%N A119356 Numbers k such that A000330(k) is squarefree.
%C A119356 The numbers of terms that do not exceed 10^k, for k = 1, 2, ..., are 8, 53, 504, 5029, 50187, 501925, 5019527, 50194688, 501948054, 5019478733, ... . Conjecture: The asymptotic density of this sequence is 4 * Product_{p prime} (1 - 3/p^2) = 4 * A206256 = 0.50194792... . - _Amiram Eldar_, Sep 24 2024
%H A119356 Robert Israel, <a href="/A119356/b119356.txt">Table of n, a(n) for n = 1..10000</a>
%e A119356 10 is a term because 10*11*(2*10+1)/6 = 5*7*11 is squarefree.
%p A119356 filter:= n -> numtheory:-issqrfree(n*(n+1)*(2*n+1)/6):
%p A119356 select(filter, [$1..200]); # _Robert Israel_, Aug 04 2020
%t A119356 Select[Range[126],SquareFreeQ[#(#+1)(2#+1)/6]&] (* _James C. McMahon_, Sep 15 2024 *)
%o A119356 (PARI) lista(nn) = {for (n=1, nn, if (issquarefree(n*(n+1)*(2*n+1)/6), print1(n, ", ")););} \\ _Michel Marcus_, May 18 2013
%Y A119356 Cf. A000330, A005117, A172186 (subsequence), A206256,
%K A119356 nonn
%O A119356 1,2
%A A119356 _Zak Seidov_, May 16 2006