A013726 a(n) = 21^(2*n + 1).
21, 9261, 4084101, 1801088541, 794280046581, 350277500542221, 154472377739119461, 68122318582951682301, 30041942495081691894741, 13248496640331026125580781, 5842587018385982521381124421, 2576580875108218291929075869661, 1136272165922724266740722458520501
Offset: 0
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).
Programs
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Magma
[21^(2*n+1): n in [0..15]]; // Vincenzo Librandi, Jun 26 2011
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Maple
seq(21^(2*n+1),n=0..10); # Nathaniel Johnston, Jun 25 2011
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Mathematica
Table[21^(2 n + 1), {n, 0, 15}] (* Wesley Ivan Hurt, Feb 10 2014 *) -
PARI
a(n)=21^(2*n+1) \\ Charles R Greathouse IV, Jul 11 2016
Formula
From Philippe Deléham, Nov 28 2008: (Start)
a(n) = 441*a(n-1); a(0)=21.
G.f.: 21/(1-441*x). (End)
From Elmo R. Oliveira, Jul 10 2025: (Start)
E.g.f.: 21*exp(441*x).