Enumeration of derangements with descents in prescribed positions

Niklas Eriksen*, Ragnar Freij, Johan Wästlund

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review

13 Citations (Scopus)

Abstract

We enumerate derangements with descents in prescribed positions. A generating function was given by Guo-Niu Han and Guoce Xin in 2007. We give a combinatorial proof of this result, and derive several explicit formulas. To this end, we consider fixed point A-coloured permutations, which are easily enumerated. Several formulae regarding these numbers are given, as well as a generalisation of Euler's difference tables. We also prove that except in a trivial special case, if a permutation π is chosen uniformly among all permutations on n elements, the events that π has descents in a set S of positions, and that π is a derangement, are positively correlated.

Original languageEnglish
Article numberR32
Number of pages19
JournalThe Electronic Journal of Combinatorics
Volume16
Issue number1
Publication statusPublished - 4 Mar 2009
MoE publication typeA1 Journal article-refereed

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