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.

1, 18, 306, 5202, 88281, 1498176, 25424928, 431474688, 7322358456, 124264377216, 2108833575552, 35788044422016, 607342437246528, 10306929088604160, 174914151758088192, 2968387598501627904, 50375140298107596288, 854893330417826832384, 14508001408391876911104

Offset: 0

Author

John Cannon and N. J. A. Sloane, Dec 03 2009

Keywords

• nonn

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.

Links

• Index entries for linear recurrences with constant coefficients, signature (16,16,16,-136).

Programs

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

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).

Extensions

More terms from Jinyuan Wang, Mar 23 2020