For ten points, identify these numbers which have two distinct postive divisors.
Barban's constant and Murata's constant are de ned as products over these numbers. Pépin's theorem gives conditions for Fermat numbers to hold this property. If the radix of a numeral system has this property, then there are an in nite number of integers with this property ending with each nonzero digit. Bertrand's postulate, which was proved by Chebyshev and later by   ErdÂ®s, states that for any integer n there is always at least one number with this property between n and 2n. These numbers are all congruent to 1 or 5 mod 6. For ten points, identify these numbers which have two distinct postive divisors.
Barban's constant and Murata's constant are de ned as products over these numbers.
prime numbers [accept word forms like primality for the property]