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Journal of the Ramanujan Mathematical Society

Volume 30, Issue 3, September 2015  pp. 331–348.

Hyperelliptic curves over Fq and Gaussian hypergeometric series

Authors:  Rupam Barman and Gautam Kalita
Author institution:Department of Mathematics, Indian Institute of Technology, Hauz Khas, New Delhi 110 016, India

Summary:  Let d ≥ 2 be an integer. Denote by Ed and E'd the hyperelliptic curves over Fq given by Ed : y2 = xd + ax + b and E'd: y2 = xd + ax d - 1 + b, respectively. We explicitly find the number of Fq-points on Ed and E'd in terms of special values of dFd - 1 and d - 1 F d - 2 Gaussian hypergeometric series with characters of orders d - 1, d, 2(d - 1), 2d, and 2d(d - 1) as parameters. This gives a solution to a problem posed by Ken Ono [17, p. 204] on special values of n + 1 Fn Gaussian hypergeometric series for n > 2. We also show that the results of Lennon [14] and the authors [4] on trace of Frobenius of elliptic curves follow from the main results.


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