A binomial-hypergeometric identity for graph-count coefficients

For integers g1g\geq 1, 0\ell\geq 0, and j1j\geq 1, let (nr)\binom{n}{r} denote the binomial coefficient, let 2F1{}_2F_1 denote the Gauss hypergeometric function, and let the product over mm be taken for 0mj10\leq m\leq j-1. The binomial-hypergeometric identity. The following identity is conjectured:

j!2+2g1((2g2)++jj)2F1(j,2j22g(+j);1)=k=1+2g(+2g1k1)m=0j12(2m+k).j!\,2^{\ell+2g-1}\binom{(2g-2)+\ell+j}{j}{}_2F_1\left(\begin{matrix}-j,-2j\\2-2g-(\ell+j)\end{matrix};-1\right)=\sum_{k=1}^{\ell+2g}\binom{\ell+2g-1}{k-1}\prod_{m=0}^{j-1}2(2m+k).

The authors verified the identity for 0200\leq\ell\leq20 and 1g,j201\leq g,j\leq20 and leave a general proof for future analysis; it arises by comparing two formulations of the graph counts N4,z(g,j){\mathcal N}_{4,z}(g,j), although equality of the resulting linear combinations does not itself require equality of their coefficients.

Sources & referencesView supporting material

Primary source

Nicholas Ercolani, Joceline Lega and Brandon Tippings, “Non-recursive Counts of Graphs on Surfaces”, arXiv:2210.00671 (2023).

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