Journal of Integer Sequences, Vol. 18 (2015), Article 15.10.3

Binary Words Avoiding x xR x and Strongly Unimodal Sequences


James Currie and Narad Rampersad
Department of Mathematics and Statistics
University of Winnipeg
515 Portage Avenue
Winnipeg, Manitoba R3B 2E9
Canada

Abstract:

In previous work, Currie and Rampersad showed that the growth of the number of binary words avoiding the pattern x x xR was intermediate between polynomial and exponential. We now show that the same result holds for the growth of the number of binary words avoiding the pattern x xR x . Curiously, the analysis for x xR x is much simpler than that for x x xR. We derive our results by giving a bijection between the set of binary words avoiding x xR x and a class of sequences closely related to the class of "strongly unimodal sequences".


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(Concerned with sequences A022567 A261204.)


Received August 12 2015; revised version received August 24 2015. Published in Journal of Integer Sequences, September 14 2015.


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