A029697 Number of words of length 2n in the 6 transpositions of S[ 4 ] equivalent to the identity.

6, 120, 3936, 140160, 5039616, 181401600, 6530359296, 235092541440, 8463329918976, 304679870791680, 10968475323334656, 394865111539384320, 14215144015015182336, 511745184538935951360, 18422826643395251798016, 663221759162203294924800

Offset

1,1

Links

Vincenzo Librandi, Table of n, a(n) for n = 1..300

Index entries for linear recurrences with constant coefficients, signature (40,-144).

Formula

a(n) = (9*4^n+36^n)/12.

a(n) = 40*a(n-1)-144*a(n-2). - Colin Barker, May 28 2015

G.f.: -6*x*(20*x-1) / ((4*x-1)*(36*x-1)). - Colin Barker, May 28 2015

Prog

(Magma) [(9*4^n+36^n)/12: n in [1..15]]; // Vincenzo Librandi, Jun 30 2011
(PARI) Vec(-6*x*(20*x-1) / ((4*x-1)*(36*x-1)) + O(x^100)) \\ Colin Barker, May 28 2015

Crossrefs

Sequence in context: A075844 A356506 A354429 * A248045 A280627 A196688

Adjacent sequences: A029694 A029695 A029696 * A029698 A029699 A029700

Keyword

nonn,easy

Author

Paolo Dominici (pl.dm(AT)libero.it)

Status

approved