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A163145 Number of reduced words of length n in Coxeter group on 21 generators S_i with relations (S_i)^2 = (S_i S_j)^4 = I. 0
1, 21, 420, 8400, 167790, 3351600, 66948210, 1337288400, 26712295890, 533577313500, 10658190898110, 212897044846500, 4252612111884990, 84945799915397400, 1696789816099808010, 33893325895893882600, 677018172425014524090, 13523417772619230573300 (list; graph; refs; listen; history; text; internal format)
OFFSET
0,2
COMMENTS
The initial terms coincide with those of A170740, although the two sequences are eventually different.
Computed with MAGMA using commands similar to those used to compute A154638.
LINKS
FORMULA
G.f.: (t^4 + 2*t^3 + 2*t^2 + 2*t + 1)/(190*t^4 - 19*t^3 - 19*t^2 - 19*t + 1).
MATHEMATICA
coxG[{4, 190, -19}] (* The coxG program is at A169452 *) (* Harvey P. Dale, Mar 25 2019 *)
PROG
(PARI) Vec((t^4 + 2*t^3 + 2*t^2 + 2*t + 1)/(190*t^4 - 19*t^3 - 19*t^2 - 19*t + 1) + O(t^20)) \\ Jinyuan Wang, Mar 23 2020
CROSSREFS
Sequence in context: A083043 A162807 A097833 * A163503 A163977 A164634
KEYWORD
nonn
AUTHOR
John Cannon and N. J. A. Sloane, Dec 03 2009
EXTENSIONS
More terms from Jinyuan Wang, Mar 23 2020
STATUS
approved

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Last modified March 28 12:59 EDT 2024. Contains 371254 sequences. (Running on oeis4.)