A013725 a(n) = 20^(2*n + 1).

20, 8000, 3200000, 1280000000, 512000000000, 204800000000000, 81920000000000000, 32768000000000000000, 13107200000000000000000, 5242880000000000000000000, 2097152000000000000000000000, 838860800000000000000000000000, 335544320000000000000000000000000

Offset: 0

Author

N. J. A. Sloane

Keywords

• nonn
• easy

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 (400).

Crossrefs

Bisection of A009964 (20^n).

Cf. A004171, A005408, A013708-A013724, A013726-A013729.

Programs

Magma

[20^(2*n+1): n in [0..15]]; // Vincenzo Librandi, Jun 26 2011

Maple

seq(20^(2*n+1),n=0..10); # Nathaniel Johnston, Jun 25 2011

Mathematica

NestList[400*# &, 20, 15] (* Paolo Xausa, Jul 12 2025 *)

PARI

a(n)=20^(2*n+1) \\ Charles R Greathouse IV, Jul 11 2016

Formula

From Philippe Deléham, Nov 28 2008: (Start)

a(n) = 400*a(n-1); a(0)=20.

G.f.: 20/(1-400*x). (End)

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

E.g.f.: 20*exp(400*x).

a(n) = A004171(n)*A013715(n) = A009964(A005408(n)). (End)