OFFSET
0,2
COMMENTS
a(n) is the number of words of length 2n in the letters a,t,t^(-1) that equal the identity of the lamplighter group Z_2 wr Z = <a,t | a^2=1, [a,t^(-k)at^k]=1 for all k >.
Walks on this group can be seen as operations on an infinite tape of 0's and 1's where each step is either a right shift, left shift or toggles the current element. a(n) is then the number of sequences of 2n such moves which return the tape to the initial position.
LINKS
Andrew Elvey Price, Table of n, a(n) for n = 0..500
Andrew Elvey Price and A. J. Guttmann, Numerical studies of Thompson's group F and related groups, arXiv:1706.07571 [math.GR], 2017.
D. Revelle, Heat kernel asymptotics on the lamplighter group, Electronic Communications in Probability 8 (2003), 142-154.
Wikipedia, Lamplighter group
CROSSREFS
KEYWORD
nonn,walk
AUTHOR
Andrew Elvey Price, Jan 13 2023
STATUS
approved