A164666 Number of reduced words of length n in Coxeter group on 30 generators S_i with relations (S_i)^2 = (S_i S_j)^7 = I.

1, 30, 870, 25230, 731670, 21218430, 615334470, 17844699195, 517496264040, 15007391291760, 435214336864440, 12621215461767360, 366015239479512840, 10614441686465394960, 307818801412722798030, 8926745023620530422680

Offset

0,2

Comments

The initial terms coincide with those of A170749, 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..15.

Index entries for linear recurrences with constant coefficients, signature (28,28,28,28,28,28,-406).

Formula

G.f.: (t^7 + 2*t^6 + 2*t^5 + 2*t^4 + 2*t^3 + 2*t^2 + 2*t + 1)/(406*t^7 - 28*t^6 - 28*t^5 - 28*t^4 - 28*t^3 - 28*t^2 - 28*t + 1).

Crossrefs

Sequence in context: A163208 A163552 A164027 * A164983 A165515 A166026

Adjacent sequences: A164663 A164664 A164665 * A164667 A164668 A164669

Keyword

nonn

Author

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

Status

approved