Abstract
Consider the set of those binary words with no non-empty factors of the form
xxx^R. Du, Mousavi, Schaeffer, and Shallit asked whether this set of words grows
polynomially or exponentially with length. In this paper, we demonstrate the
existence of upper and lower bounds of the form n^{lg n+o(lg n)} on the number of
such words of length n, where lg n denotes the base-2 logarithm of n.
