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

0,2

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

Table of n, a(n) for n=0..19.

Index entries for linear recurrences with constant coefficients, signature (13,13,13,-91).

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).

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 *)

Crossrefs

Cf. A170734.

Sequence in context: A000483 A162785 A076139 * A163440 A163962 A164626

Adjacent sequences: A163088 A163089 A163090 * A163092 A163093 A163094

Keyword

nonn

Author

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

Extensions

More terms from Jinyuan Wang, Mar 22 2020

Status

approved