Polynomiality conjecture for Hankel determinants of generalized Catalan powers

From papers

Let G(x,r)G(x,r) be the generalized generating function used in the paper, and write Hn(G(x,r))H_n(G(x,r)) for the Hankel determinant of its coefficients. For a positive integer tt, consider first r=2t+1r=2t+1. Generalized Catalan polynomiality conjecture. If r=2t+1r=2t+1 is odd and 1jr+341\leq j\leq\left\lfloor\frac{r+3}{4}\right\rfloor, then

Hrn+j(G(x,r)),Hrn+t+j(G(x,r)),Hrn+t+2j(G(x,r)),Hrn+r+1j(G(x,r))H_{rn+j}(G(x,r)),\quad H_{rn+t+j}(G(x,r)),\quad H_{rn+t+2-j}(G(x,r)),\quad H_{rn+r+1-j}(G(x,r))

are all polynomials in nn of degree (2j1)(t+1j)(2j-1)(t+1-j). If r=2tr=2t is even and 1jt1\leq j\leq t, then

(1)tnHrn+j(G(x,r))(-1)^{tn}H_{rn+j}(G(x,r))

and

(1)tnHrn+r+1j(G(x,r))(-1)^{tn}H_{rn+r+1-j}(G(x,r))

are both polynomials in nn of degree (j1)(r+12j)(j-1)(r+1-2j). The conjecture extends the paper's polynomiality predictions to the generalized family GG; the supplied context gives no resolution, so its status remains open.

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Sources & referencesView supporting material

Primary source

Ying Wang and Guoce Xin, “Hankel determinants for convolution powers of Catalan numbers”, arXiv:1811.00248 (2018).

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