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 A261034 #26 Sep 26 2023 02:15:21
%S A261034 1,2,5,7,10,11,13,14,17,19,22,23,26,29,31,34,35,37,38,41,43,46,47,53,
%T A261034 55,58,59,61,62,65,67,70,71,73,74,77,79,82,83,85,86,89,91,94,95,97,
%U A261034 101,103,106,107,109,110,113,115,118,119,122,127,130,131
%N A261034 Numbers m such that 3*m is squarefree.
%C A261034 These are the numbers from A005117 that are not divisible by 3. See the Maple program by _Robert Israel_. - _Wolfdieter Lang_, Aug 21 2015
%C A261034 Squarefree numbers divisible by 3: 3, 6, 15, 21, 30, 33, 39, 42, 51, 57, 66, 69, 78, 87, 93, 102, ...
%F A261034 a(n) ~ 2*Pi^2*n/9. - _Charles R Greathouse IV_, Aug 07 2015
%F A261034 Sum_{n>=1} 1/a(n)^s = (3^s)*zeta(s)/((1+3^s)*zeta(2*s)), s>1. - _Amiram Eldar_, Sep 26 2023
%e A261034 10 is in this sequence because 3*10 = 30 is squarefree.
%p A261034 select(numtheory:-issqrfree, [seq(seq(3*i+j,j=1..2),i=0..1000)]); # _Robert Israel_, Aug 07 2015
%t A261034 Select[Range[0, 200], SquareFreeQ[3 #] &] (* _Vincenzo Librandi_, Aug 08 2015 *)
%o A261034 (Magma) [n: n in [1..200] | IsSquarefree(3*n)];
%o A261034 (PARI) is(n)=n%3 && issquarefree(n) \\ _Charles R Greathouse IV_, Aug 07 2015
%Y A261034 Cf. A045344, A088245.
%Y A261034 Numbers m such that k*m is squarefree: A005117 (k = 1), A056911 (k = 2), this sequence (k = 3), A274546 (k = 5), A276378 (k = 6).
%K A261034 nonn,easy
%O A261034 1,2
%A A261034 _Juri-Stepan Gerasimov_, Aug 07 2015
%E A261034 Corrected and extended by _Vincenzo Librandi_, Aug 08 2015