OFFSET
0,2
COMMENTS
The group is presented by <a, t | 1 = [a, t^(-k) a t^k], for all k>.
LINKS
Walter Parry, Growth series of some wreath products, Trans. Amer. Math. Soc. 331 (1992), 751-759.
Index entries for linear recurrences with constant coefficients, signature (4, -2, -4, -4, 4, 6, 4, 1).
FORMULA
G.f.: (1-x)^3 (1+x)^3 (1+x^2) / ((1-2x-x^2)(1-x-x^2-x^3)^2).
EXAMPLE
a(2)=12, since the elements of length 2 are a^2, at, at^-1, a^-2, a^-1t, a^-1t^-1, ta, ta^-1, t^2, t^-1a, t^-1a^-1, t^-2.
CROSSREFS
KEYWORD
nonn
AUTHOR
Zoran Sunic, Nov 08 2017
STATUS
approved