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Proofs of conjectures on Ramanujan-type series of level 3

Number Theory 2023-10-10 v1

Abstract

A Ramanujan-type series satisfies 1π=n=0(12)n(1s)n(11s)n(1)n3zn(a+bn), \frac{1}{\pi} = \sum_{n=0}^{\infty} \frac{\left( \frac{1}{2} \right)_{n} \left( \frac{1}{s} \right)_{n} \left(1 - \frac{1}{s} \right)_{n} }{ \left( 1 \right)_{n}^{3} } z^{n} (a + b n), where s{2,3,4,6}s \in \{ 2, 3, 4, 6 \}, and where aa, bb, and zz are real algebraic numbers. The level 33 case whereby s=3s = 3 has been considered as the most mysterious and the most challenging, out of all possible values for ss, and this motivates the development of new techniques for constructing Ramanujan-type series of level 33. Chan and Liaw introduced an alternating analogue of the Borwein brothers' identity for Ramanujan-type series of level 33; subsequently, Chan, Liaw, and Tian formulated another proof of the Chan-Liaw identity, via the use of Ramanujan's class invariant. Using the elliptic lambda function and the elliptic alpha function, we prove, using a limiting case of the Kummer-Goursat transformation, a new identity for evaluating zz, aa, and bb for Ramanujan-type series such that s=3s = 3 and z<0z < 0, and we apply this new identity to prove three conjectured formulas for quadratic-irrational, Ramanujan-type series that had been discovered via numerical experiments with Maple in 2012 by Aldawoud. We also apply our identity to prove a new Ramanujan-type series of level 33 with quartic values for z<0z < 0, aa, and bb.

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Cite

@article{arxiv.2310.05112,
  title  = {Proofs of conjectures on Ramanujan-type series of level 3},
  author = {John M. Campbell},
  journal= {arXiv preprint arXiv:2310.05112},
  year   = {2023}
}

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