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A163104
Number of reduced words of length n in Coxeter group on 18 generators S_i with relations (S_i)^2 = (S_i S_j)^4 = I.
0
1, 18, 306, 5202, 88281, 1498176, 25424928, 431474688, 7322358456, 124264377216, 2108833575552, 35788044422016, 607342437246528, 10306929088604160, 174914151758088192, 2968387598501627904, 50375140298107596288, 854893330417826832384, 14508001408391876911104
OFFSET
0,2
COMMENTS
The initial terms coincide with those of A170737, 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)/(136*t^4 - 16*t^3 - 16*t^2 - 16*t + 1).
PROG
(PARI) Vec((t^4 + 2*t^3 + 2*t^2 + 2*t + 1)/(136*t^4 - 16*t^3 - 16*t^2 - 16*t + 1) + O(t^20)) \\ Jinyuan Wang, Mar 23 2020
CROSSREFS
Sequence in context: A162804 A097831 A342885 * A163452 A163967 A164630
KEYWORD
nonn
AUTHOR
John Cannon and N. J. A. Sloane, Dec 03 2009
EXTENSIONS
More terms from Jinyuan Wang, Mar 23 2020
STATUS
approved