Problem #23

There are 2^n "words" of length n using an alphabet consisting of the letters a and b. For example, the words of length 2 are aa, ab, ba, and bb. It is easy to find a word of length 5 so that, reading from left to right, every two letter word appears; reading aabba yields aa, ab, bb, and ba.

Can you find a word of length 19 so that, reading from left to right, every four letter word appears?

SOURCE: Eric Shade

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