Upper bound for the number of privileged words

05/25/2022
by   Josef Rukavicka, et al.
0

A non-empty word w is a border of a word u if | w|<| u| and w is both a prefix and a suffix of u. A word u is privileged if | u|≤ 1 or if u has a privileged border w that appears exactly twice in u. Peltomäki (2016) presented the following open problem: “Give a nontrivial upper bound for B(n)”, where B(n) denotes the number of privileged words of length n. Let ln^[0](n)=n and let ln^[j](n)=ln(ln^[j-1](n)), where j,n are positive integers. We show that if q>1 is a size of the alphabet and j≥ 3 is an integer then there are constants α_j and n_j such that B(n)≤α_jq^n√(lnn)/√(n)ln^[j](n)∏_i=2^j-1√(ln^[i](n))n≥ n_j This result improves the upper bound of Rukavicka (2020).

READ FULL TEXT

Please sign up or login with your details

Forgot password? Click here to reset

Sign in with Google

×

Use your Google Account to sign in to DeepAI

×

Consider DeepAI Pro