Abstract:
We prove that the number of parameters D up to a fixed x≥2 such that the fundamental solution εD to the Pell equation T2−DU2=1 lies between D12+α1 and D12+α2 is greater than √xlog2x up to a constant as long as α1<α2 and α1<3/2. The starting point of the proof is a reduction step already used by the authors in earlier works. This approach is amenable to analytic methods. Along the same lines, and inspired by the work of Dirichlet, we show that the set of parameters D≤x for which logεD is larger than D14 has a cardinality essentially larger than x14log2x.
Citation:
Étienne Fouvry, Florent Jouve, “Fundamental solutions to Pell equation with prescribed size”, Number theory, algebra, and analysis, Collected papers. Dedicated to Professor Anatolii Alekseevich Karatsuba on the occasion of his 75th birthday, Trudy Mat. Inst. Steklova, 276, MAIK Nauka/Interperiodica, Moscow, 2012, 46–56; Proc. Steklov Inst. Math., 276 (2012), 40–50