Regular prime

In number theory, a prime number \( p \) is called a **regular prime** if it does not divide the numerator of the binomial coefficients \( \binom{n}{k} \) for any integers \( n \) and \( k \) where both \( k \) and \( n-k \) are less than \( p \). In simpler terms, a regular prime is one that behaves "nicely" with respect to these combinatorial quantities.