A013726 a(n) = 21^(2*n + 1).

21, 9261, 4084101, 1801088541, 794280046581, 350277500542221, 154472377739119461, 68122318582951682301, 30041942495081691894741, 13248496640331026125580781, 5842587018385982521381124421, 2576580875108218291929075869661, 1136272165922724266740722458520501

Offset

0,1

Links

Vincenzo Librandi, Table of n, a(n) for n = 0..200

Tanya Khovanova, Recursive Sequences.

Index entries for linear recurrences with constant coefficients, signature (441).

Formula

From Philippe Deléham, Nov 28 2008: (Start)

a(n) = 441*a(n-1); a(0)=21.

G.f.: 21/(1-441*x). (End)

a(n) = A009965(A005408(n)). - Wesley Ivan Hurt, Feb 10 2014

From Elmo R. Oliveira, Jul 10 2025: (Start)

E.g.f.: 21*exp(441*x).

a(n) = A013708(n)*A013712(n). (End)

Maple

seq(21^(2*n+1), n=0..10); # Nathaniel Johnston, Jun 25 2011

Mathematica

Table[21^(2 n + 1), {n, 0, 15}] (* Wesley Ivan Hurt, Feb 10 2014 *)
NestList[441#&, 21, 20] (* Harvey P. Dale, Oct 12 2025 *)

Prog

(Magma) [21^(2*n+1): n in [0..15]]; // Vincenzo Librandi, Jun 26 2011
(PARI) a(n)=21^(2*n+1) \\ Charles R Greathouse IV, Jul 11 2016

Crossrefs

Bisection of A009965 (21^n).

Cf. A005408, A013708-A013725, A013727-A013729.

Sequence in context: A176446 A380792 A135823 * A159358 A048914 A046183

Adjacent sequences: A013723 A013724 A013725 * A013727 A013728 A013729

Keyword

nonn,easy

Author

N. J. A. Sloane

Status

approved