A193303 Squarefree numbers multiplied by powers of three.

1, 2, 3, 5, 6, 7, 9, 10, 11, 13, 14, 15, 17, 18, 19, 21, 22, 23, 26, 27, 29, 30, 31, 33, 34, 35, 37, 38, 39, 41, 42, 43, 45, 46, 47, 51, 53, 54, 55, 57, 58, 59, 61, 62, 63, 65, 66, 67, 69, 70, 71, 73, 74, 77, 78, 79, 81, 82, 83, 85, 86, 87, 89, 90, 91, 93

Offset

1,2

Comments

The asymptotic density of this sequence is 27/(4*Pi^2). - Amiram Eldar, Oct 01 2020

Links

Amiram Eldar, Table of n, a(n) for n = 1..10000

Mathematica

lim = 102; sf = Select[Range[lim], SquareFreeQ]; lim3 = 3^Range[0, Log[3, lim]]; Select[Union[Flatten[Outer[Times, sf, lim3]]], # <= lim &]

Prog

(PARI) is(n)=issquarefree(n/3^valuation(n, 3)) \\ Charles R Greathouse IV, Jul 31 2011

Crossrefs

Cf. A000244 (powers of 3), A005117 (squarefree numbers).

Sequence in context: A048103 A276078 A387181 * A285465 A092418 A004195

Adjacent sequences: A193300 A193301 A193302 * A193304 A193305 A193306

Keyword

nonn,easy

Author

José María Grau Ribas, Jul 21 2011

Status

approved