Place the letters of the English alphabet (capitals) in a row and count five letters inward from either end. You will arrive at letters which are quite similar to their neighbors (on their inside), E to F and V to U. There is one other adjacent pair of letters resembling each other -- M and N. Because M and N mark the center of the alphabet, the three couples EF-MN-UV induce a natural pairing of the entire alphabet.
Zerger, Monte J.
"The Alphabet and the Golden Ratio,"
Word Ways: Vol. 27
, Article 8.
Available at: https://digitalcommons.butler.edu/wordways/vol27/iss3/8