English

Springer Numbers and Arnold Families Revisited

Combinatorics 2021-11-02 v1

Abstract

For the calculation of Springer numbers (of root systems) of type BnB_n and DnD_n, Arnold introduced a signed analogue of alternating permutations, called βn\beta_n-snakes, and derived recurrence relations for enumerating the βn\beta_n-snakes starting with kk. The results are presented in the form of double triangular arrays (vn,kv_{n,k}) of integers, 1kn1\le |k|\le n. An Arnold family is a sequence of sets of such objects as βn\beta_n-snakes that are counted by (vn,k)(v_{n,k}). As a refinement of Arnold's result, we give analogous arrays of polynomials, defined by recurrence, for the calculation of the polynomials associated with successive derivatives of tanx\tan x and secx\sec x, established by Hoffman. Moreover, we provide some new Arnold families of combinatorial objects that realize the polynomial arrays, which are signed variants of Andr\'{e} permutations and Simsun permutations.

Keywords

Cite

@article{arxiv.2111.00888,
  title  = {Springer Numbers and Arnold Families Revisited},
  author = {Sen-Peng Eu and Tung-Shan Fu},
  journal= {arXiv preprint arXiv:2111.00888},
  year   = {2021}
}

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24 pages