Starry lines

At the Data String Research Institute, a crisis has occurred. After developing an algorithm that destroys strings, all existing strings were eliminated, and now there is an urgent need to create new ones. However, completely random strings are undesirable, so Andryusha is aiming for aesthetic appeal in the new strings. His latest task is dedicated to so-called starry strings.

A string is said to be $c$-starry (where $c$ is some character) if it is either empty, or has the form S_1cS_2c\ldots S_{k-1}cS_k for some integer k \ge 2. In this form, each S_i is a $d$-starry string of equal length, where $d$ is the character immediately following $c$ in the alphabet. The only exception is for $z$-starry strings, which are defined as strings consisting only of the letter $z$ (including the empty string).

A starry string is any string that is $c$-starry for some letter $c$ of the Latin alphabet (i.e., for some lowercase English letter $c$).

For example, the string ccbccbccbcc is $b$-starry, but the strings ccbccbccbc and aabccbaa are not.

Andryusha is wondering how many starry strings of a given length exist. Write a program that determines the number of such strings of length $n$.