Lara K. Pudwell
This engaging article takes the reader on a journey in which a graphical
representation of permutations provokes an interesting counting problem
with surprising results. The article begins with a clear definition and visualiza-
tion of permutations. A well-chosen permutation of the digits 1-9 illustrates
patterns within permutations, prompting the question of how many permu-
tations avoid a given pattern. The article continues with progressively more
complicated examples which prepare the reader for two surprising examples
and an unsolved problem.
There are unexpected connections made to famous landmarks as the
journey unfolds. A computer science problem from Donald Knuth motivates
the counting question. A nicely illustrated explanation of a recursive solution
of one counting problem leads directly to the Catalan numbers. A related
problem is solved with a familiar recurrence relation, the generator of the
Fibonacci numbers. The article concludes with some intriguing clues to send
the reader on a journey into more complicated and unsolved problems.
This video was recorded at the 2023 MAA MAthFest conference where the speaker recived the
Trevor Evans Award, established by the Board of Governors in 1992 and
first awarded in 1996. It is made to authors of expository articles accessible to
undergraduates and published in Math Horizons. The Award is named for
Trevor Evans, a distinguished mathematician, teacher, and writer at Emory
University.
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