We give an instance of Stembridge's q = -1 phenomenon for pattern- avoiding permutations. In particular, we show that setting q = -1 in the generating function for 132-avoiding permutations with respect to the statistic rsg returns the number of 132-avoiding involutions.
Eric S. Egge, Department of Mathematics, Carleton College
"A q = -1 Phenomenon for Pattern-Avoiding Permutations,"
Rose-Hulman Undergraduate Mathematics Journal: Vol. 12
, Article 2.
Available at: http://scholar.rose-hulman.edu/rhumj/vol12/iss2/2