A164644 Number of reduced words of length n in Coxeter group on 27 generators S_i with relations (S_i)^2 = (S_i S_j)^7 = I.

1, 27, 702, 18252, 474552, 12338352, 320797152, 8340725601, 216858856500, 5638330032075, 146596574673900, 3811510781360100, 99099276151168800, 2576581071661350000, 66991105048200214050, 1741768658063341610625

Offset

0,2

Comments

The initial terms coincide with those of A170746, 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 (25,25,25,25,25,25,-325).

Formula

G.f.: (t^7 + 2*t^6 + 2*t^5 + 2*t^4 + 2*t^3 + 2*t^2 + 2*t + 1)/(325*t^7 - 25*t^6 - 25*t^5 - 25*t^4 - 25*t^3 - 25*t^2 - 25*t + 1).

Crossrefs

Sequence in context: A163179 A163527 A164017 * A164969 A165445 A165979

Adjacent sequences: A164641 A164642 A164643 * A164645 A164646 A164647

Keyword

nonn

Author

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

Status

approved