Enveloping expansion for series 33

Let series #33 in Table have t=1t=-1, and let Rn\mathcal{R}_n and Fn\mathcal{F}_n be the quantities associated with this series. Let cjc_j be the coefficients defined by Theorem. Enveloping-expansion conjecture. Theorem is also valid for series #33, and, for every LNL\in\mathbb N, its expansion satisfies

j=04L1cjnj<RnFn<j=04L+1cjnj.\sum_{j=0}^{4L-1}\frac{c_j}{n^j} < \frac{\mathcal{R}_n}{\mathcal{F}_n} < \sum_{j=0}^{4L+1}\frac{c_j}{n^j}.

The conjecture concerns the exceptional case t=1t=-1, which lies outside the proof's hypothesis t<1|t|<1. The displayed inequalities assert an enveloping expansion and give numerical control of the truncated asymptotic series for this particular hypergeometric series.

Sources & referencesView supporting material

Primary source

Lorenz Milla and Chao-Ping Chen, “Asymptotic expansions of truncated hypergeometric series for 1/π”, arXiv:2401.05419 (2024).

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