 Bertrand's postulate

For every integer $n>1$, there is a prime number strictly between $n$ and $2n$. This supplies cyclic prime moduli comparable to an integer interval's length in additive combinatorics.

Bertrand's postulate, also known as Bertrand's conjecture, states that for any integer \( n > 1 \), there exists at least one prime number \( p \) such that \( n < p < 2n \). In other words, there is always at least one prime number between any integer \( n \) and its double \( 2n \). This conjecture was first proposed by the Russian mathematician Joseph Bertrand in 1845.