A366288 Numbers k such that 3*k is not squarefree.

3, 4, 6, 8, 9, 12, 15, 16, 18, 20, 21, 24, 25, 27, 28, 30, 32, 33, 36, 39, 40, 42, 44, 45, 48, 49, 50, 51, 52, 54, 56, 57, 60, 63, 64, 66, 68, 69, 72, 75, 76, 78, 80, 81, 84, 87, 88, 90, 92, 93, 96, 98, 99, 100, 102, 104, 105, 108, 111, 112, 114, 116, 117, 120, 121, 123, 124, 125, 126, 128, 129, 132, 135, 136, 138

Offset

1,1

Comments

The asymptotic density of this sequence is 1 - 9/(2*Pi^2). - Amiram Eldar, Oct 08 2023

Links

Table of n, a(n) for n=1..75.

Mathematica

Select[Range[140], !SquareFreeQ[3*#] &] (* Amiram Eldar, Oct 08 2023 *)

Prog

(PARI) isA366288(n) = !issquarefree(3*n);

Crossrefs

Complement of A261034.

Union of A013929 and A008585 (after its initial 0).

Positions of zeros in A156277, in A359377, and in A365428.

Cf. A366290 (subsequence).

Sequence in context: A192519 A036446 A284469 * A059267 A362670 A355200

Adjacent sequences: A366285 A366286 A366287 * A366289 A366290 A366291

Keyword

nonn,easy

Author

Antti Karttunen, Oct 07 2023

Status

approved