%I
%S 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,
%T 35,37,38,39,41,42,43,45,46,47,51,53,54,55,57,58,59,61,62,63,65,66,67,
%U 69,70,71,73,74,77,78,79,81,82,83,85,86,87,89,90,91,93
%N Squarefree numbers multiplied by powers of three.
%t lim = 102; sf = Select[Range[lim], SquareFreeQ]; lim3 = 3^Range[0, Log[3, lim]]; Select[Union[Flatten[Outer[Times, sf, lim3]]], # <= lim &]
%o (PARI) is(n)=issquarefree(n/3^valuation(n,3)) \\ _Charles R Greathouse IV_, Jul 31 2011
%K nonn
%O 1,2
%A _José María Grau Ribas_, Jul 21 2011
