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

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A164696 Number of reduced words of length n in Coxeter group on 3 generators S_i with relations (S_i)^2 = (S_i S_j)^8 = I. 0
1, 3, 6, 12, 24, 48, 96, 192, 381, 756, 1503, 2988, 5940, 11808, 23472, 46656, 92742, 184353, 366456, 728439, 1447986, 2878296, 5721456, 11373072, 22607316, 44938668, 89328777, 177567132, 352966731, 701624856, 1394685096, 2772345504 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

The initial terms coincide with those of A003945, although the two sequences are eventually different.

Computed with MAGMA using commands similar to those used to compute A154638.

LINKS

Table of n, a(n) for n=0..31.

Index entries for linear recurrences with constant coefficients, signature (1, 1, 1, 1, 1, 1, 1, -1).

FORMULA

G.f. (t^8 + 2*t^7 + 2*t^6 + 2*t^5 + 2*t^4 + 2*t^3 + 2*t^2 + 2*t + 1)/(t^8 - t^7 -

t^6 - t^5 - t^4 - t^3 - t^2 - t + 1)

MATHEMATICA

With[{num=Total[2t^Range[7]]+t^8+1, den=Total[-t^Range[7]]+t^8+1}, CoefficientList[ Series[ num/den, {t, 0, 40}], t]] (* Harvey P. Dale, Aug 05 2011 *)

CROSSREFS

Sequence in context: A164352 A115829 A115805 * A165183 A046944 A165745

Adjacent sequences:  A164693 A164694 A164695 * A164697 A164698 A164699

KEYWORD

nonn

AUTHOR

John Cannon and N. J. A. Sloane, Dec 03 2009

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 April 24 04:45 EDT 2019. Contains 322412 sequences. (Running on oeis4.)