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A163149
Number of reduced words of length n in Coxeter group on 22 generators S_i with relations (S_i)^2 = (S_i S_j)^4 = I.
0
1, 22, 462, 9702, 203511, 4268880, 89544840, 1878307200, 39399681090, 826454197800, 17335839305400, 363639419173800, 7627760320511100, 160001156198268000, 3356210592504924000, 70400425902447564000
OFFSET
0,2
COMMENTS
The initial terms coincide with those of A170741, although the two sequences are eventually different.
Computed with MAGMA using commands similar to those used to compute A154638.
FORMULA
G.f.: (t^4 + 2*t^3 + 2*t^2 + 2*t + 1)/(210*t^4 - 20*t^3 - 20*t^2 - 20*t + 1).
a(n) = -210*a(n-4) + 20*Sum_{k=1..3} a(n-k). - Wesley Ivan Hurt, May 05 2021
MATHEMATICA
CoefficientList[Series[(t^4 + 2 t^3 + 2 t^2 + 2 t + 1)/(210 t^4 - 20 t^3 - 20 t^2 - 20 t + 1), {t, 0, 16}], t] (* Jinyuan Wang, Mar 23 2020 *)
CROSSREFS
Sequence in context: A162808 A212335 A342887 * A163514 A163988 A164635
KEYWORD
nonn
AUTHOR
John Cannon and N. J. A. Sloane, Dec 03 2009
STATUS
approved