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Conditional bounds for the least quadratic non-residue and related problems. (English) Zbl 1326.11058

Math. Comput. 84, No. 295, 2391-2412 (2015); corrigendum ibid. 86, No. 307, 2551-2554 (2017).
Let \(q>1\) be a positive number and let \(G = (\mathbb Z/q\mathbb Z)^*\) denote the group of reduced residues \(\pmod{q}\) and let \(H\) be a proper subgroup of \(G\). Assuming the generalized Riemann hypothesis the authors prove:
(1)
If \(q \geq 3000\) is an integer then the least prime \(\ell\) with \(\ell\not |q\) and \(\ell\) not lying in the subgroup \(H\) satisfies the bound \(\ell\leq (\log q+B(q))^2\) where \(B(q)\) is explicitly given.
(2)
If the index \(h=|G:H|\geq4\) then the least prime \(p\) not in \(H\) satisfies \(p<(\alpha(h)+o(1))(\log q)^2\) again with \(\alpha(h)\) explicitly given.
(3)
If \(q\geq 20000\) and \(h>1\) then the smallest prime \(p\) lying in a given coset \(aH\) is either \(\leq 10^9\) or \(\leq\left((h-1)\log q+3(h+1)+(5/2)(\log\log q)^2\right)^2\) (the proof gives actually a more precise estimate).
(4)
New explicit upper and lower bounds for \(L\)-values at the edge of the critical strip and explicit bounds for the class number of imaginary quadratic fields.
If \(H=G\) or \(H=\{1\}\), that is for the least quadratic non-residue or for the least prime in an arithmetic progression, the above estimates are improved using computer computations for all \(q\geq 5\), or \(q>3\), respectively.

MSC:

11N60 Distribution functions associated with additive and positive multiplicative functions
11R42 Zeta functions and \(L\)-functions of number fields

References:

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