Bertrand 's postulate states that if n ) 3 is an integer , then there always exists at least one prime number p with n ( p ( 2n â ' 2 . Bertrand 's postulate ( actually a theorem ) states that if n ) 3 is an integer , then there always exists at least one prime number p with n 1 there is always at least one prime p such that n ( p ( 2n .