Abstract
An expansion formula of the classical Gaussian \(_2F_1\)-series in terms of Legendre polynomials due to Holdeman (J Math Phys 11:114–117, 1970) is extended to generalized hypergeometric series of higher order. Its special cases together with Holdeman’s formula are employed to derive explicit Fourier–Legendre series for forty \(_2F_1\)-functions. By applying a “product integration" method to these \(_2F_1\)-expressions, we establish numerous identities for double series involving multinomial coefficients, including a remarkable formula for \(\zeta (3)/\pi ^2\) found recently by the second author.
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The authors are sincerely grateful to anonymous reviewers for their careful reading, critical comments, and valuable suggestions that contributed significantly to improving the manuscript during the revision.
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Chu, W., Campbell, J.M. Expansions over Legendre polynomials and infinite double series identities. Ramanujan J 60, 317–353 (2023). https://doi.org/10.1007/s11139-022-00663-4
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DOI: https://doi.org/10.1007/s11139-022-00663-4
Keywords
- Hypergeometric series
- Legendre polynomial
- Fourier–Legendre series
- Product integration
- Gamma function
- Central binomial coefficient
- Multinomial coefficient