Decreasing pattern minimizes avoidance among alternating permutations

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Let An(q)A_n(q) denote the set of alternating permutations of length nn avoiding the pattern qq, and let SkS_k be the symmetric group on kk letters. Alternating-avoidance minimization conjecture. For all positive integers k,nk,n and all q∈Skq\in S_k with q≠k(k−1)(k−2)⋯1q\ne k(k-1)(k-2)\cdots1,

∣An(q)∣≥∣An(k(k−1)(k−2)⋯1)∣.|A_n(q)|\ge |A_n(k(k-1)(k-2)\cdots1)|.

If n≥2k−2n\ge2k-2 is even, then the inequality is strict. The claim is motivated by brute-force enumerations, is known for k=3k=3, and the case n=2k−2n=2k-2 was proved in the cited corollary.

References

Primary source

Nihal Gowravaram and Ravi Jagadeesan, “Beyond alternating permutations: Pattern avoidance in Young diagrams and tableaux”, arXiv:1301.6796 (2013).

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