login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A056120 a(n) = (3^3)*4^(n-3); a(0)=1, a(1)=1. 1
1, 1, 7, 27, 108, 432, 1728, 6912, 27648, 110592, 442368, 1769472, 7077888, 28311552, 113246208, 452984832, 1811939328, 7247757312, 28991029248, 115964116992, 463856467968, 1855425871872 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

For n>=3, a(n) is equal to the number of functions f:{1,2,...,n}->{1,2,3,4} such that for fixed, different x_1, x_2, x_3 in {1,2,...,n} and fixed y_1, y_2, y_3 in {1,2,3,4} we have f(x_i)<>y_i, (i=1,2,...,n). - Milan Janjic, May 13 2007

LINKS

Table of n, a(n) for n=0..21.

Milan Janjic, Enumerative Formulas for Some Functions on Finite Sets

Index entries for linear recurrences with constant coefficients, signature (4).

FORMULA

a(n)=4a(n-1)+[(-1)^n]*C(3, 3-n). G.f.(x)=(1-x)^3/(1-4x).

CROSSREFS

Cf. A055841.

First differences of A002063.

Sequence in context: A054485 A090856 A055917 * A255278 A294262 A048711

Adjacent sequences:  A056117 A056118 A056119 * A056121 A056122 A056123

KEYWORD

easy,nonn

AUTHOR

Barry E. Williams, Jul 05 2000

EXTENSIONS

a(21) corrected by R. J. Mathar, Dec 03 2014

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified February 15 20:32 EST 2019. Contains 320138 sequences. (Running on oeis4.)