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

From papers

A valleyless-tieless parking function of length nn is a parking function (a1,,an)(a_1,\ldots,a_n) with no index 1in11\leq i\leq n-1 such that ai=ai+1a_i=a_{i+1} and no index 2in12\leq i\leq n-1 such that ai1>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=Fn3.|{\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.

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Sources & referencesView supporting material

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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