|
| |
|
|
A163124
|
|
Number of reduced words of length n in Coxeter group on 20 generators S_i with relations (S_i)^2 = (S_i S_j)^4 = I.
|
|
0
|
|
|
|
1, 20, 380, 7220, 136990, 2599200, 49316400, 935712000, 17753871510, 336855735180, 6391382632020, 121267853544780, 2300893742387430, 43656351283440360, 828320305398630840, 15716259104684097960
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
|
OFFSET
|
0,2
|
|
|
COMMENTS
|
The initial terms coincide with those of A170739, 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..15.
Index entries for linear recurrences with constant coefficients, signature (18, 18, 18, -171).
|
|
|
FORMULA
|
G.f.: (t^4 + 2*t^3 + 2*t^2 + 2*t + 1)/(171*t^4 - 18*t^3 - 18*t^2 - 18*t + 1)
|
|
|
MATHEMATICA
|
coxG[{4, 171, -18}] (* The coxG program is at A169452 *) (* Harvey P. Dale, Dec 14 2015 *)
|
|
|
CROSSREFS
|
Sequence in context: A084329 A097832 A342886 * A163454 A163969 A164633
Adjacent sequences: A163121 A163122 A163123 * A163125 A163126 A163127
|
|
|
KEYWORD
|
nonn
|
|
|
AUTHOR
|
John Cannon and N. J. A. Sloane, Dec 03 2009
|
|
|
STATUS
|
approved
|
| |
|
|
