Question

Assume that the initials of any person are written using only the 26 uppercase letters and are at least two letters long (that everyone has at least a first name and a last name) and at most five letters long (e.g., someone might have three middle names, in which case they would have five initials). How many different strings of initials (of length two, three, four, or five) are there in which not all the letters are the same? Note: Your count should exclude strings such as JJJ and CC, because all of the letters are the same in these strings, but should include initials such as CCJ.

Answer 1