Improved Estimates for the Number of Privileged Words
Jeremy Nicholson and Narad Rampersad
Department of Mathematics and Statistics
University of Winnipeg
515 Portage Avenue
Winnipeg, Manitoba R3B 2E9
Canada
Abstract:
In combinatorics on words, a word w of length n
over an alphabet of
size q is said to be privileged if n ≤ 1,
or if n ≥ 2 and w has a
privileged border that occurs exactly twice in w. Forsyth,
Jayakumar and Shallit proved that there exist at least
2n-5/n2 privileged
binary words of length n.
Using the work of Guibas and Odlyzko, we prove that there are
constants c and n0 such that for
n ≥ n0,
there are at least
cqn/(n(logq n)2)
privileged words of length n over an alphabet of size q.
Thus, for n sufficiently large,
we improve the earlier bound determined by Forsyth,
Jayakumar and Shallit, and generalize it for all q.
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(Concerned with sequence
A231208.)
Received January 23 2018; revised version received May 2 2018.
Published in Journal of Integer Sequences, May 7 2018.
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