A005051 a(n) = 8*3^n.

8, 24, 72, 216, 648, 1944, 5832, 17496, 52488, 157464, 472392, 1417176, 4251528, 12754584, 38263752, 114791256, 344373768, 1033121304, 3099363912, 9298091736, 27894275208, 83682825624, 251048476872, 753145430616, 2259436291848, 6778308875544, 20334926626632

Offset

0,1

Comments

For n>=3, a(n-3) is equal to the number of functions f:{1,2,...,n}->{1,2,3} such that for fixed, different x_1, x_2, x_3 in {1,2,...,n} and fixed y_1, y_2, y_3 in {1,2,3} we have f(x_i)<>y_i, (i=1,2,3). - Milan Janjic, May 13 2007

Links

Vincenzo Librandi, Table of n, a(n) for n = 0..300

Milan Janjic, Enumerative Formulas for Some Functions on Finite Sets

Tanya Khovanova, Recursive Sequences

Index entries for linear recurrences with constant coefficients, signature (3).

Formula

a(n) = 3*a(n-1). G.f.: 8/(1-3*x). - Colin Barker, Jul 02 2012

Mathematica

8*3^Range[0, 60] (* Vladimir Joseph Stephan Orlovsky, Jun 09 2011 *)

Prog

(Magma) [8*3^n: n in [0..30]]; // Vincenzo Librandi, Jun 10 2011
(PARI) a(n)=8*3^n \\ Charles R Greathouse IV, Sep 28 2015

Crossrefs

Sequence in context: A343546 A199911 A083583 * A303402 A078158 A221906

Adjacent sequences: A005048 A005049 A005050 * A005052 A005053 A005054

Keyword

nonn,easy

Author

N. J. A. Sloane

Status

approved