Fixed-point product formula conjecture for evacuation of Kreweras words

Let n1n\geq 1, and let Evac\operatorname{{Evac}} and Evac\operatorname{{Evac}}^{*} denote the two evacuation operations on Kreweras words of length 3n3n. For a word ww, consider the fixed-point conditions Evac(w)=w\operatorname{{Evac}}^{*}(w)=w and Evac(w)=w\operatorname{{Evac}}(w)=w.

Evacuation fixed-point conjecture. For all n1n\geq 1, the number of Kreweras words of length 3n3n satisfying Evac(w)=w\operatorname{{Evac}}^{*}(w)=w is

3n/24n/2j=1n/2(3j1)j=1n/2(3j2)(n+1)!.\frac{3^{\lfloor n/2 \rfloor} 4^{\lceil n/2 \rceil} \prod_{j=1}^{\lfloor n/2 \rfloor}(3j-1) \prod_{j=1}^{\lceil n/2 \rceil}(3j-2) }{(n+1)!}.

The number satisfying Evac(w)=w\operatorname{{Evac}}(w)=w is the same when nn is even and is 00 when nn is odd. These formulas provide product expressions for the evacuation fixed points, while their status beyond the conjecture is not established in the supplied text.

Sources & referencesView supporting material

Primary source

Sam Hopkins and Martin Rubey, “Promotion of Kreweras words”, arXiv:2005.14031 (2021).

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