1641 - Count Sorted Vowel Strings.

Medium

Given an integer n, return the number of strings of length n that consist only of vowels (a, e, i, o, u) and are lexicographically sorted.

A string s is lexicographically sorted if for all valid i, s[i] is the same as or comes before s[i+1] in the alphabet.

Example 1:

Input: n = 1

Output: 5

Explanation: The 5 sorted strings that consist of vowels only are ["a","e","i","o","u"].

Example 2:

Input: n = 2

Output: 15

Explanation: The 15 sorted strings that consist of vowels only are

"aa","ae","ai","ao","au","ee","ei","eo","eu","ii","io","iu","oo","ou","uu".

Note that "ea" is not a valid string since 'e' comes after 'a' in the alphabet.

Example 3:

Input: n = 33

Output: 66045

Constraints:

• 1 <= n <= 50