it's worth reading just for one of the best book in-jokes ever - see the introductory part "Notes on the Exercises" of Volume 2 "Seminumerical Algorithms"

3. [M50] Prove that when n is an integer, n > 2, the equation xn + yn = zn has no solution in positive integers x, y, z.

Knuth's book was published in 1973. The initial solution to this exercise was solved by a then Princeton professor in 1993 and was finalized by same professor and his former student by 1995.