A147675 Divide by 2, multiply by 4, repeat.

10, 5, 20, 10, 40, 20, 80, 40, 160, 80, 320, 160, 640, 320, 1280, 640, 2560, 1280, 5120, 2560, 10240, 5120, 20480, 10240, 40960, 20480, 81920, 40960, 163840, 81920, 327680, 163840, 655360, 327680, 1310720, 655360, 2621440, 1310720, 5242880

Offset

1,1

Comments

A147675-A147678 are from a quiz that someone asked me to help them with.

Links

Table of n, a(n) for n=1..39.

Index entries for linear recurrences with constant coefficients, signature (0,2).

Formula

From R. J. Mathar, Apr 22 2009: (Start)

a(n) = 2*a(n-2) = 5*A135530(n-1).

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

From Amiram Eldar, Feb 02 2024: (Start)

Sum_{n>=1} 1/a(n) = 3/5.

Sum_{n>=1} (-1)^n/a(n) = 1/5. (End)

Mathematica

LinearRecurrence[{0, 2}, {10, 5}, 50] (* Paolo Xausa, Jan 30 2024 *)

Crossrefs

Cf. A020714, A135530.

Sequence in context: A280154 A040093 A046797 * A070291 A361671 A183132

Adjacent sequences: A147672 A147673 A147674 * A147676 A147677 A147678

Keyword

nonn,easy

Author

N. J. A. Sloane, Apr 21 2009

Extensions

More terms from R. J. Mathar, Apr 22 2009

Status

approved