A note on the total number of cycles of even and odd permutations

TL;DR

This paper proves a bijective relationship showing the difference in total cycle counts between even and odd permutations of [n], and establishes a more general combinatorial identity involving permutation cycles.

Contribution

It provides a bijective proof of the difference in total cycles between even and odd permutations and introduces a new general identity involving cycle counts and factorials.

Findings

Difference in total cycles of even and odd permutations is (-1)^n(n-2)!

Established a new combinatorial identity involving cycle counts and factorials

Proved the identity bijectively for all n and k

Abstract

We prove bijectively that the total number of cycles of all even permutations of $[n]=\{1,2,...,n\}$ and the total number of cycles of all odd permutations of $[n]$ differ by $(-1)^n(n-2)!$, which was stated as an open problem by Mikl\'{o}s B\'{o}na. We also prove bijectively the following more general identity: $$\sum_{i=1}^n c(n,i)\cdot i \cdot (-k)^{i-1} = (-1)^k k! (n-k-1)!,$$ where $c(n,i)$ denotes the number of permutations of $[n]$ with $i$ cycles.