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arXiv · 2608.19276

${}_5F_4$ evaluations and a family of $π^2+\log^2$ identities

Cetin Hakimoglu-Brown
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Abstract

We evaluate the series $\sum_{n\ge1} z^n\big/\!\big(n^2\binom{4n}{n}\big)$, equal to $-\tfrac{z}{4}\,{}_5F_4\!\left(1,1,1,\tfrac43,\tfrac53;\tfrac54,\tfrac32,\tfrac74,2;\tfrac{27z}{256}\right)$, in closed form at an infinite family of algebraic points indexed by a rational angle $θ=jπ/N$. Each value equals $c\,π^2$ plus a universal rational quadratic form in three logarithms, with $c=-\tfrac13\left(1-\tfrac{2j}{N}\right)^2$. This is the quartic-base case reached but not evaluated by D'Aurizio and Di Trani. The proof is self-contained: an exact integer factor relating two weights, followed by Landen's identity, reduces the integral to a sum of squared logarithms.

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Cetin Hakimoglu-Brown. 2026-08-18. ${}_5F_4$ evaluations and a family of $π^2+\log^2$ identities. https://arxiv.org/abs/2608.19276

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