Entringer number conjecture for 000-avoiding inversion sequences

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The Entringer numbers dn,kd_{n,k} count down/up permutations of [n+1][n+1] whose first entry is k+1k+1, and satisfy

dn,k=dn,k−1+dn−1,n−k.d_{n,k}=d_{n,k-1}+d_{n-1,n-k}.

An Entringer number conjecture asserts that, for n≥1n\geq 1 and 0≤k≤n−10\leq k\leq n-1, dn,kd_{n,k} is the number of inversion sequences e∈In(000)e\in\mathbf{I}_n(000) with last entry en=k−1e_n=k-1.

This conjecture proposes a direct interpretation of the Entringer numbers in terms of 000-avoiding inversion sequences; the source reports it as suggested by computations, and no resolution is provided.

References

Primary source

Sylvie Corteel, Megan A. Martinez, Carla D. Savage and Michael Weselcouch, “Patterns in Inversion Sequences I”, arXiv:1510.05434 (2016).

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