A366288 - OEIS

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

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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