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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