Let's say a word has four letters. At least one must be a vowel (stir). At least one must be a consonant (lieu).
5C1 * 21C1 * 26C1 * 26C1 * 4! = 5*21*26*26*24 = 1.7 million possible four letter words. Some repeat letters (loll).
Then add 1,2,3,5,6,7,however many letters you want as the max.