The name Agamemnon is composed of three consecutive sets of three letters in which the first and third letters in each triplet is the same. There are a handful of such words in the Merriam-Webster Unabridged Dictionary (Second or Third Editions): AGAMEMNON, MIMULUSES, ILICACAEAE, SUSUHUNAN, COCCACEAE and the doubtful MIMICISMS ("morbid tendencies to mimicry"). A search for analogous twelve-letter words in Levine's pattern word lists proved unsuccessful, although a few one-letter misses did surface: IMITATRESSES, IRIDODONESIS (and its listed plural), VIVIDIALYSIS (and its inferred plural).
Wolpow, Edward R.
Word Ways: Vol. 13
, Article 11.
Available at: http://digitalcommons.butler.edu/wordways/vol13/iss2/11