Odd-length alternating-permutation equivalence of the six remaining patterns

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Let Am(p)A_m(p) denote the set of alternating permutations of length mm that avoid the pattern pp. Two patterns are equivalent for odd-length alternating permutations when their avoidance classes have equal cardinality for every odd length. Remaining odd-class conjecture. The patterns 23142314, 41324132, 24132413, 31423142, 14231423, and 32413241 are equivalent for odd-length alternating permutations; equivalently, for all n≥0n\geq 0 their avoidance classes have a common cardinality:

∣A2n+1(2314)∣=∣A2n+1(4132)∣=∣A2n+1(2413)∣=∣A2n+1(3142)∣=∣A2n+1(1423)∣=∣A2n+1(3241)∣.|A_{2n+1}(2314)|=|A_{2n+1}(4132)|=|A_{2n+1}(2413)|=|A_{2n+1}(3142)|=|A_{2n+1}(1423)|=|A_{2n+1}(3241)|.

The paper identifies this as the only other possible odd-length equivalence not ruled out by numerical data, and the conjecture remains open.

References

Primary source

Joel Brewster Lewis, “Generating trees and pattern avoidance in alternating permutations”, arXiv:1005.4046 (2010).

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