Palindromes in starlike trees

In this note, we obtain an upper bound on the maximum number of distinct non-empty palindromes in starlike trees. This bound implies, in particular, that there are at most 4 n distinct non-empty palindromes in a starlike tree with three branches each of length n. For such starlike trees labelled with a binary alphabet, we sharpen the upper bound to 4 n − 1 and conjecture that the actual maximum is 4 n − 2. It is intriguing that this simple conjecture seems difficult to prove, in contrast to the proof of the bound

Palindromes in circular words

There is a very short and beautiful proof that the number of distinct non-empty palindromes in a word of length n is at most n. In this paper we show, with a very complicated proof, that the number of distinct non-empty palindromes with length at most n in a circular word of length n is less than 5n/3. For n divisible by 3 we present circular words of length n containing 5n/3 -2 distinct palindromes, so the bound is almost sharp. The paper finishes with some open problems