Czechoslovak Mathematical Journal, Vol. 67, No. 2, pp. 439-455, 2017

Density of solutions to quadratic congruences

Neha Prabhu

Received December 31, 2015.  First published May 5, 2017.

Abstract:  A classical result in number theory is Dirichlet's theorem on the density of primes in an arithmetic progression. We prove a similar result for numbers with exactly $k$ prime factors for $k>1$. Building upon a proof by E. M. Wright in 1954, we compute the natural density of such numbers where each prime satisfies a congruence condition. As an application, we obtain the density of squarefree $n\leq x$ with $k$ prime factors such that a fixed quadratic equation has exactly $2^k$ solutions modulo $n$.
Keywords:  Dirichlet's theorem; asymptotic density; primes in arithmetic progression; squarefree number
Classification MSC:  11D45, 11B25, 11N37
DOI:  10.21136/CMJ.2017.0712-15

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Affiliations:   Neha Prabhu, Indian Institute of Science Education and Research, Dr Homi Bhabha Rd, NCL Colony, Pashan, Pune, Maharashtra 411008, India, e-mail:

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