login
A165214
Number of reduced words of length n in Coxeter group on 7 generators S_i with relations (S_i)^2 = (S_i S_j)^9 = I.
0
1, 7, 42, 252, 1512, 9072, 54432, 326592, 1959552, 11757291, 70543620, 423260985, 2539561500, 15237342540, 91423896480, 548542426320, 3291248842560, 19747458763200, 118484546826660, 710906046446925, 4265428871616150
OFFSET
0,2
COMMENTS
The initial terms coincide with those of A003949, although the two sequences are eventually different.
Computed with MAGMA using commands similar to those used to compute A154638.
FORMULA
G.f. (t^9 + 2*t^8 + 2*t^7 + 2*t^6 + 2*t^5 + 2*t^4 + 2*t^3 + 2*t^2 + 2*t +
1)/(15*t^9 - 5*t^8 - 5*t^7 - 5*t^6 - 5*t^5 - 5*t^4 - 5*t^3 - 5*t^2 - 5*t
+ 1)
MATHEMATICA
coxG[{9, 15, -5}] (* The coxG program is at A169452 *) (* Harvey P. Dale, Nov 02 2015 *)
CROSSREFS
Sequence in context: A163923 A164369 A164742 * A165782 A166365 A166518
KEYWORD
nonn
AUTHOR
John Cannon and N. J. A. Sloane, Dec 03 2009
STATUS
approved