Stanley's equidistribution conjecture for alternating permutations and derangements

Let [n]={1,,n}[n]=\{1,\dots,n\} and let SnS_n be the set of permutations of [n][n]. A permutation a1ana_1\cdots a_n is alternating if a1>a2<a3>a4<a_1>a_2<a_3>a_4<\dots, and it is reverse alternating if a1<a2>a3<a4>a_1<a_2>a_3<a_4>\dots. Let dk(n)d_k(n) and dk(n)d_k^*(n) denote, respectively, the numbers of alternating and reverse alternating permutations in SnS_n with kk fixed points. Let DnD_n be the number of derangements in SnS_n, that is, permutations with no fixed points.

Stanley's conjecture. For n4n\geq4 and n5n\geq5, respectively,

dn/2(n)=Dn/2,d_{\lceil n/2\rceil}(n)=D_{\lfloor n/2\rfloor},

and

d(n+1)/2(n)=D(n1)/2.d^*_{\lceil (n+1)/2\rceil}(n)=D_{\lfloor (n-1)/2\rfloor}.

This conjecture asserts an equidistribution between derangements and alternating or reverse alternating permutations having the maximal possible number of fixed points. The source presents it as Stanley's conjecture; no resolution status is supplied here.

Sources & referencesView supporting material

Primary source

Robin Chapman and Lauren K. Williams, “A conjecture of Stanley on alternating permutations”, arXiv:math/0702808 (2007).

Progress summary

Never refreshed

Nothing recorded yet. Refresh searches the literature and the public web for attempts on this problem, and writes the first summary here.

Solutions 0

No solutions have been posted yet.