Asymptotic product formula conjecture for weighted binary-sum Hankel determinants

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Let H(n,1)\mathcal H(n,1) denote the Hankel determinant studied in the paper. For each fixed integer k0k\geq 0, consider the values with index n=2m+kn=2^m+k. Asymptotic product formula conjecture. There exist integers m0=m0(k)0m_0=m_0(k)\geq 0 and r=r(k)0r=r(k)\geq 0, a sign εk{±1}\varepsilon_k\in\{\pm 1\}, a polynomial Pk(X)Q[X]P_k(X)\in\mathbb{Q}[X], and a constant ckQc_k\in\mathbb{Q} such that, for all mm0(k)m\geq m_0(k),

H(2m+k,1)=εkPk(2m)(ck+j=1mr2j12j1)j=1mr(2j1)2mrj.\mathcal H(2^m+k,1)=\varepsilon_k P_k(2^m)\left(c_k+\sum_{j=1}^{m-r}\frac{2^{j-1}}{2^j-1}\right)\prod_{j=1}^{m-r}(2^j-1)^{2^{m-r-j}}.

Moreover, the polynomial Pk(2m)P_k(2^m) and the shift r(k)r(k) are determined by the binary expansion of kk and the sequence of branches encountered when repeatedly applying the determinant recurrence theorem. This extends the explicit formulas known for k=1,0,1k=-1,0,1; the general form and its dependence on the binary expansion remain conjectural.

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Primary source

Bartosz Sobolewski and Maciej Ulas, “Hankel determinants of weighted binary sums of digits”, arXiv:2607.09376 (2026).

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