报告题目：(q,t) -Catalan numbers and gamma expansions
报告人:Bin Han 博士(法国里昂第一大学)
报告时间:2019年7月12日上午10:00-11：00
报告地点:苏大本部精正楼307
报告摘要: We first prove several new interpretations of a kind of (q,t)-Catalan numbers along with their corresponding γ-expansions using pattern avoiding permutations. Secondly, we give a complete characterization of certain (−1)-phenomenon for each subset of permutations avoiding a single pattern of length three, and discuss their q-analogues utilizing the newly obtained q-γ-expansions, as well as the continued fraction of a quint-variate generating function due to Shin and the Zeng. Moreover, we enumerate the alternating permutations avoiding simultaneously two patterns, namely (2413,3142) and (1342,2431), of length four, and consider such (−1)-phenomenon for these two subsets as well.
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