What is the Dirichlet density of all primes whose least residue modulo $24$ is strictly less than $8$? I don't understand the meaning of least residue I know the Dirichlet density of a set of primes that conference to $a \bmod m$ is equal to 1/ Euler(m) where the greatest common divisor between $a$ and $m$ is $1$.
Any help is appreciated In the note it is 3/Euler(24) But why