Dirichlet's Theorem

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Dirichlet's Theorem may refer to:

Dirichlet's Approximation Theorem

Diophantine equations


Let $\alpha, x \in \R$.


Then there exist integers $a, q$ such that:

$\gcd \set {a, q} = 1$, $1 \le q \le x$

and:

$\size {\alpha - \dfrac a q} \le \dfrac 1 {q x}$


Dirichlet's Theorem on Arithmetic Sequences

Number Theory, specifically prime numbers


Let $a, q$ be coprime integers.

Let $\PP_{a, q}$ be the set of primes $p$ such that $p \equiv a \pmod q$.


Then $\PP_{a, q}$ has Dirichlet density:

$\map \phi q^{-1}$

where $\phi$ is Euler's phi function.


In particular, $\PP_{a, q}$ is infinite.


Dirichlet's Unit Theorem

Algebraic number theory and ring theory

Dirichlet's Unit Theorem


Source of Name

This entry was named for Johann Peter Gustav Lejeune Dirichlet.