On k-abelian palindromes
: Julien Cassaigne, Juhani Karhumäki, Svetlana Puzynina
Publisher: Elsevier Inc.
: 2018
: Information and Computation
: Information and Computation
: 260
: 89
: 98
: 10
: 0890-5401
: 1090-2651
DOI: https://doi.org/10.1016/j.ic.2018.04.001
A word is called a palindrome if it is equal to its reversal. In the paper we consider a k-abelian modification of this notion. Two words are called k-abelian equivalent if they contain the same number of occurrences of each factor of length at most k. We say that a word is a k-abelian palindrome if it is k-abelian equivalent to its reversal. A question we deal with is the following: how many distinct palindromes can a word contain? It is well known that a word of length n can contain at most n+1
distinct palindromes as its factors; such words are called rich. On the other hand, there exist infinite words containing only finitely many distinct palindromes as their factors; such words are called poor. We show that in the k-abelian case there exist infinite words containing finitely many distinct k-abelian palindromic factors. For rich words we show that there exist finite words of length n containing Θ(n2)
distinct k-abelian palindromes as their factors.