A group of two successive letters is called a bigram. There are 26 different bigrams beginning with each letter of the alphabet making a total of 26x26 = 676 different bigrams. The word BIGRAM itself incorporates the five bigrams BI, IG, GR, RA and AM, and none of them is repeated. COCOa, DEriDE, IOnizatIOn and tORpOR, on the other hand, each contain a pair of identical bigrams and there are thousands of these double bigram words ("Miami Words" in the February 2000 Word Ways are a special kind of double bigram word). Somewhat less common are words such as fINgerprINtINg with a triple bigram set. In turn, there are even fewer words which contain a set of more than three identical bigrams. INtestINoINtestINal (DOR) is a quadruple example.
Word Ways: Vol. 33
, Article 2.
Available at: http://digitalcommons.butler.edu/wordways/vol33/iss4/2