A163091 Number of reduced words of length n in Coxeter group on 15 generators S_i with relations (S_i)^2 = (S_i S_j)^4 = I.

1, 15, 210, 2940, 41055, 573300, 8005725, 111793500, 1561106820, 21799608285, 304414090890, 4250899269435, 59360407871310, 828920611657320, 11575213262103855, 161638593827703720, 2257153663002754425, 31519345335542489880, 440142444293996873520, 6146237150764726493205

Offset: 0

Author

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

Keywords

• nonn

Comments

The initial terms coincide with those of A170734, 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 (13,13,13,-91).

Crossrefs

Cf. A170734.

Programs

Mathematica

CoefficientList[Series[(t^4 + 2 t^3 + 2 t^2 + 2 t + 1)/(91 t^4 - 13 t^3 - 13 t^2 - 13 t + 1), {t, 0, 20}], t] (* Jinyuan Wang, Mar 22 2020 *)

Formula

G.f.: (t^4 + 2*t^3 + 2*t^2 + 2*t + 1)/(91*t^4 - 13*t^3 - 13*t^2 - 13*t + 1).

Extensions

More terms from Jinyuan Wang, Mar 22 2020