Siegel–Walfisz theorem

In analytic number theory, the Siegel–Walfisz theorem was obtained by Arnold Walfisz^[1] as an application of a theorem by Carl Ludwig Siegel^[2] to primes in arithmetic progressions.

Statement

Define

\psi (x;q,a)=\sum _{{n\leq x \atop n\equiv a{\pmod q}}}\Lambda (n),

where $\Lambda$ denotes the von Mangoldt function and φ to be Euler's totient function.

Then the theorem states that given any real number N there exists a positive constant C_N depending only on N such that

\psi (x;q,a)={\frac {x}{\varphi (q)}}+O\left(x\exp \left(-C_{N}(\log x)^{{\frac {1}{2}}}\right)\right),

whenever (a, q) = 1 and

q\leq (\log x)^{N}.

Remarks

The constant C_N is not effectively computable because Siegel's theorem is ineffective.

From the theorem we can deduce the following bound regarding the prime number theorem for arithmetic progressions: If, for (a,q)=1, by $\pi (x;q,a)$ we denote the number of primes less than or equal to x which are congruent to a mod q, then

\pi (x;q,a)={\frac {{{\rm {Li}}}(x)}{\varphi (q)}}+O\left(x\exp \left(-{\frac {C_{N}}{2}}(\log x)^{{\frac {1}{2}}}\right)\right),

where N, a, q, C_N and φ are as in the theorem, and Li denotes the offset logarithmic integral.

References

↑ Walfisz, Arnold (1936). "Zur additiven Zahlentheorie. II" [On additive number theory. II]. Mathematische Zeitschrift (in German). 40 (1): 592–607. MR 1545584. doi:10.1007/BF01218882.
↑ Siegel, Carl Ludwig (1935). "Über die Classenzahl quadratischer Zahlkörper" [On the class numbers of quadratic fields]. Acta Arithmetica (in German). 1 (1): 83–86.

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