Explicit Hankel transform conjecture for the cubic Catalan family

From papers

Let c(x)c(x) denote the Catalan generating function and define a sequence by

Fα(x)=1xx2αx31xx2x3c(x3(1xx2αx3)(1xx2x3)2).F_\alpha(x)=\frac{1-x-x^2-\alpha x^3}{1-x-x^2-x^3}c\left(\frac{x^3(1-x-x^2-\alpha x^3)}{(1-x-x^2-x^3)^2}\right).

Define

An(α)=[xn]1+(α2)x2(α2)x3+(4α5)x5(α1)(α2)x81+3x3(α2)x6,A_n(\alpha)=[x^n]\frac{1+(\alpha-2)x^2-(\alpha-2)x^3+(4\alpha-5)x^5-(\alpha-1)(\alpha-2)x^8}{1+3x^3-(\alpha-2)x^6}, Bn=[xn]x(1x+2x22x3+3x43x5+x6)(1x)2(1x3).B_n=[x^n]\frac{x(1-x+2x^2-2x^3+3x^4-3x^5+x^6)}{(1-x)^2(1-x^3)}.

Cubic-family Hankel-transform conjecture. The Hankel transform of the sequence with generating function Fα(x)F_\alpha(x) is hn=An(α)(2α)Bnh_n=A_n(\alpha)(2-\alpha)^{B_n}. The formula is given as a further conjectural pattern after the quadratic-family examples.

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Sources & referencesView supporting material

Primary source

Paul Barry, “Generalized Catalan recurrences, Riordan arrays, elliptic curves, and orthogonal polynomials”, arXiv:1910.00875 (2019).

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