A163225 Number of reduced words of length n in Coxeter group on 42 generators S_i with relations (S_i)^2 = (S_i S_j)^4 = I.

1, 42, 1722, 70602, 2893821, 118611360, 4861619280, 199267084800, 8167519684380, 334768674223200, 13721431911885600, 562411325222191200, 23052003666190808400, 944850946620132384000, 38727362890294069152000

Offset: 0

Author

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

Keywords

• nonn

Comments

The initial terms coincide with those of A170761, 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 (40, 40, 40, -820).

Formula

G.f.: (t^4 + 2*t^3 + 2*t^2 + 2*t + 1)/(820*t^4 - 40*t^3 - 40*t^2 - 40*t + 1)