%I #25 Jan 17 2022 04:46:00

%S 1,2,3,4,6,7,8,12,14,16,24,28,32,48,56,64,96,112,128,192,224,256,384,

%T 448,512,768,896,1024,1536,1792,2048,3072,3584,4096,6144,7168,8192,

%U 12288,14336,16384,24576,28672,32768,49152,57344,65536,98304,114688,131072

%N Numbers of the form 2^k times 1, 3 or 7.

%H Vincenzo Librandi, <a href="/A029748/b029748.txt">Table of n, a(n) for n = 0..1000</a>

%H <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (0,0,2).

%F From _Colin Barker_, Jul 19 2013: (Start)

%F a(n) = 2*a(n-3) for n>5.

%F G.f.: -(x^5+2*x^4+2*x^3+3*x^2+2*x+1) / (2*x^3-1). (End)

%F Sum_{n>=0} 1/a(n) = 62/21. - _Amiram Eldar_, Jan 17 2022

%t CoefficientList[Series[-(x^5 + 2 x^4 + 2 x^3 + 3 x^2 + 2 x + 1)/(2 x^3 - 1), {x, 0, 50}], x] (* _Vincenzo Librandi_, Oct 18 2013 *)

%t Sort[Flatten[#{1,3,7}&/@(2^Range[0,20])]] (* _Harvey P. Dale_, Jan 30 2014 *)

%Y Cf. A000079, A005009, A007283, A029744, A029746.

%K nonn,easy

%O 0,2

%A _N. J. A. Sloane_.

%E More terms from _Colin Barker_, Jul 19 2013