2019 BMT Individual 9
Source:
January 9, 2022
combinatorics
Problem Statement
Define an almost-palindrome as a string of letters that is not a palindrome but can become a palindrome if one of its letters is changed. For example, is an almost-palindrome because the can be changed to an to produce a palindrome, but is not an almost-palindrome because it cannot be changed into a palindrome by swapping out only one letter (both the and the are out of place). How many almost-palindromes contain fewer than letters.