A005032 a(n) = 7*3^n.

7, 21, 63, 189, 567, 1701, 5103, 15309, 45927, 137781, 413343, 1240029, 3720087, 11160261, 33480783, 100442349, 301327047, 903981141, 2711943423, 8135830269, 24407490807, 73222472421, 219667417263, 659002251789, 1977006755367, 5931020266101, 17793060798303

Offset: 0

Author

N. J. A. Sloane

Keywords

• nonn
• easy

Links

• Vincenzo Librandi, Table of n, a(n) for n = 0..1000
• Milan Janjic, Enumerative Formulas for Some Functions on Finite Sets
• Tanya Khovanova, Recursive Sequences
• Index entries for linear recurrences with constant coefficients, signature (3).

Crossrefs

Cf. A000244.

Programs

Magma

[7*3^n: n in [0..30]]; // Vincenzo Librandi, Sep 15 2011

Mathematica

7*3^Range[0, 60] (* Vladimir Joseph Stephan Orlovsky, Jun 09 2011 *)
NestList[3#&,7,30] (* Harvey P. Dale, May 05 2016 *)

PARI

a(n)=7*3^n \\ Charles R Greathouse IV, Oct 07 2015

Formula

From Vincenzo Librandi, Sep 15 2011: (Start)

G.f.: 7/(1-3*x).

a(n) = 3*a(n-1), a(0)=7. (End)

E.g.f.: 7*exp(3*x). - Stefano Spezia, Aug 28 2023