In "A Palindromic Alphabetic Insertion" (WW, Nov. 1982), we displayed a set of 3-letter palindromes of the form A-A, covering every combination from AAA, chief signet-bearer in the land of Kens, under the Egyptian king Aspalut, through to AZA, a male given name of Hebrew origin meaning "the noble."
"Another Palindromic Insertion" (WW, Aug 1992) explored the letter set A--A, giving examples for all but three of the double-letter alphabetic insertions, from AAAA, a Tahitian interjection of laughter or ridicule, to AZZA, a wadi in Iran. Examples have now been found for the missing combinations.
"Alphabetic Insertions in Five-Letter Palindromes,"
Word Ways: Vol. 48
, Article 4.
Available at: https://digitalcommons.butler.edu/wordways/vol48/iss1/4