A175805 a(n) = 21*2^n.

21, 42, 84, 168, 336, 672, 1344, 2688, 5376, 10752, 21504, 43008, 86016, 172032, 344064, 688128, 1376256, 2752512, 5505024, 11010048, 22020096, 44040192, 88080384, 176160768, 352321536, 704643072, 1409286144, 2818572288, 5637144576, 11274289152, 22548578304, 45097156608

Offset: 0

Author

Vincenzo Librandi, Dec 05 2010

Keywords

• nonn
• easy

Comments

The squares of these terms appear in A159256. - Elmo R. Oliveira, Sep 15 2024

Links

• Vincenzo Librandi, Table of n, a(n) for n = 0..1000
• Index entries for linear recurrences with constant coefficients, signature (2).

Crossrefs

Cf. A000079, A159256.

Programs

Magma

[21*2^n: n in [0..100]];

Mathematica

Table[21 2^n, {n, 0, 40}] (* Vincenzo Librandi, Jul 08 2016 *)

PARI

a(n)=21<Charles R Greathouse IV, Oct 07 2015

Formula

G.f.: 21/(1-2*x).

a(n) = 2*a(n-1). - Vincenzo Librandi, Jul 08 2016

From Elmo R. Oliveira, Sep 14 2024: (Start)

E.g.f.: 21*exp(2*x).

a(n) = 21*A000079(n). (End)