MathDB
Counting "Good Words"

Source:

December 26, 2006

Problem Statement

Define a good wordgood~word as a sequence of letters that consists only of the letters A,A, B,B, and CC −- some of these letters may not appear in the sequence −- and in which AA is never immediately followed by B,B, BB is never immediately followed by C,C, and CC is never immediately followed by A.A. How many seven-letter good words are there?
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