Bertrand's postulate

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.