A123760 Numbers whose binary expansion is 1xy100...0 where x,y = 0 or 1.

9, 11, 13, 15, 18, 22, 26, 30, 36, 44, 52, 60, 72, 88, 104, 120, 144, 176, 208, 240, 288, 352, 416, 480, 576, 704, 832, 960, 1152, 1408, 1664, 1920, 2304, 2816, 3328, 3840, 4608, 5632, 6656, 7680, 9216, 11264, 13312, 15360, 18432, 22528, 26624

Offset: 1

Author

Reinhard Zumkeller, Oct 13 2006

Keywords

• nonn
• base

Links

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

Crossrefs

Cf. A029744, A070875, A070876, A093873.

Programs

Mathematica

Union[Join @@ (Table[FromDigits[Join[#, Table[0, {n}]], 2], {n, 0, 11}] & /@ {{1, 0, 0, 1}, {1, 0, 1, 1}, {1, 1, 0, 1}, {1, 1, 1, 1}})] (* Amiram Eldar, Mar 28 2022 *)

Formula

a(n) = 2*a(n-4) for n > 4.

A093873(a(n)) = 3.

Sum_{n>=1} 1/a(n) = 4448/6435. - Amiram Eldar, Mar 28 2022