The q-tangent continued-fraction conjecture for parameter tuple (1,0,1,0)(1,0,1,0)

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Let qq be a parameter and let tan⁡q(z)\tan_q(z) denote the q-tangent function. For the parameter tuple (A,B,C,D)=(1,0,1,0)(A,B,C,D)=(1,0,1,0), consider the continued fraction

tan⁡q(z)=z[1]qq0−z2[3]qq−2−z2[5]qq1−z2[7]qq−9−z2⋱.\tan_q(z)=\cfrac{z}{[1]_q q^{0}-\cfrac{z^2}{[3]_q q^{-2}-\cfrac{z^2}{[5]_q q^{1}-\cfrac{z^2}{[7]_q q^{-9}-\cfrac{z^2}{\ddots}}}}}.

Continued-fraction conjecture. The positive powers of qq in this continued fraction follow the sequence 0,1,6,15,…0,1,6,15,\dots, given by k(2k−1)k(2k-1), while the negative powers follow 2,9,20,35,…2,9,20,35,\dots, given by (k+1)(2k−1)(k+1)(2k-1).

This conjecture proposes an explicit continued-fraction pattern for the q-tangent function in the indicated parameter case. The associated continuant polynomials are not known: the source states that the coefficients cannot presently be guessed and leaves their expansion as an open problem.

References

Primary source

Helmut Prodinger, “Combinatorics of geometrically distributed random variables: New q-tangent and q-secant numbers”, arXiv:math/9910096 (1999).

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