The Fine-number enumeration conjecture for valleyless-tieless parking functions

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A valleyless-tieless parking function of length nn is a parking function (a1,…,an)(a_1,\ldots,a_n) with no index 1≤i≤n−11\leq i\leq n-1 such that ai=ai+1a_i=a_{i+1} and no index 2≤i≤n−12\leq i\leq n-1 such that ai−1>ai<ai+1a_{i-1}>a_i<a_{i+1}. Let VTPFn{\mathrm{VTPF}}_n denote the set of valleyless-tieless parking functions of length nn, and let FiF_i be the iith Fine number. Fine-number enumeration conjecture. Valleyless-tieless parking functions of length nn are enumerated by

∣VTPFn∣=Fn−3.|{\mathrm{VTPF}}_n|=F_{n-3}.

This is presented as an open problem in the paper; the statement includes the indexing convention for the Fine numbers but gives no evidence of a resolution.

References

Primary source

Ari Cruz, Pamela E. Harris, Kimberly J. Harry, Jan Kretschmann, Matt McClinton, Alex Moon, John O. Museus and Eric Redmon, “On some discrete statistics of parking functions”, arXiv:2312.16786 (2024).

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