On Enumeration of Families of Genus Zero Permutations
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Abstract
The genus of a permutation \(\sigma \) of length n is the nonnegative integer \(g_{\sigma }\) given by \(n+1-2g_{\sigma }={\textsf {cyc}}(\sigma )+{\textsf {cyc}}(\sigma ^{-1}\zeta _n)\), where \({\textsf {cyc}}(\sigma )\) is the number of cycles of \(\sigma \) and \(\zeta _n\) is the cyclic permutation \((1,2,\ldots ,n)\). On the basis of a connection between genus zero permutations and noncrossing partitions, we enumerate the genus zero permutations with various restrictions, including André permutations, simsun permutations, and smooth permutations. Moreover, we present refined sign-balance results on genus zero permutations and their analogues restricted to connected permutations.
Keywords
Genus zero permutation Noncrossing partition André permutation Simsun permutation Smooth permutation Sign-balance identityNotes
Acknowledgements
The authors thank the referees for carefully reading the manuscript and providing helpful suggestions. This research is partially supported by Ministry of Science and Technology (MOST), Taiwan, under Grants 107-2115-M-003-009-MY3 (S.-P. Eu), 107-2115-M-153-003-MY2 (T.-S. Fu), and 108-2115-M-013-001 (C.-T. Ting).
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