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URL: https://oeis.org/A013726

⇱ A013726 - OEIS

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A013726
a(n) = 21^(2*n + 1).
3
21, 9261, 4084101, 1801088541, 794280046581, 350277500542221, 154472377739119461, 68122318582951682301, 30041942495081691894741, 13248496640331026125580781, 5842587018385982521381124421, 2576580875108218291929075869661, 1136272165922724266740722458520501
OFFSET
0,1
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).
Sequence in context: A176446 A380792 A135823 * A159358 A048914 A046183
KEYWORD
nonn,easy
STATUS
approved