Consider all possible valid English words having at least 3 letters and at most 13 letters that satisfy the following conditions:
- Each word ends with a letter that immediately follows the letter that the word begins with. (For example, if a word begins with c it must end in d), and:
- Reversing the letters we obtain another valid English word, and:
- None of the words can be proper nouns, acronyms or abbreviations, and:
- None of the words can be hyphenated like A-bomb, X-ray etc.
13 ??
