Conjectural inversion enumerations for Magog matrices

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Let Magogn\mathrm{Magog}_n denote the set of Magog matrices of size nn, and let posinv\mathrm{posinv} and inv\mathrm{inv} denote the positive inversion statistic and inversion statistic, respectively. For a statistic ss, write ∣Magogn(k s)∣|\mathrm{Magog}_n(k~s)| for the number of matrices in Magogn\mathrm{Magog}_n with statistic ss equal to kk. The conjectured enumerations are:

Inversion-enumeration conjecture.

∣Magogn(1 posinv)∣=(n2),n≥2,|\mathrm{Magog}_n(1~\mathrm{posinv})|=\binom{n}{2},\qquad n\geq 2, ∣Magogn(2 posinv)∣=2(n−12)+4(n−13)+3(n−14),n≥3,|\mathrm{Magog}_n(2~\mathrm{posinv})|=2\binom{n-1}{2}+4\binom{n-1}{3}+3\binom{n-1}{4},\qquad n\geq 3, ∣Magogn((n2)−2 posinv)∣=n(n−2),n≥3,|\mathrm{Magog}_n(\binom{n}{2}-2~\mathrm{posinv})|=n(n-2),\qquad n\geq 3, ∣Magogn((n2)−1 inv)∣=2n−n−1,|\mathrm{Magog}_n(\binom{n}{2}-1~\mathrm{inv})|=2^n-n-1,

the nnth Eulerian number. These formulas are based on numerical data; the second sequence matches OEIS sequence A090809, which counts the coefficient of a certain irreducible character of the symmetric group in a certain Kronecker power. Further verification or proofs of the enumerations remain open.

References

Primary source

Vincent Holmlund and Jessica Striker, “Totally symmetric self-complementary plane partition matrices and related polytopes”, arXiv:2312.03564 (2024).

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