(Ir)regularity of the set of primes. Since antiquity it is known that there is an infinite number of primes. The proof is simple. Suppose the set of primes P is finite. Now multiply all elements of P and add 1. The resulting number cannot be divided by any member of P, so P is incomplete. An estimation of the density of the prime numbers given by the Prime Number Theorem (see entry in Encyclopaedia Britannica on Prime Number Theorem [OIR]). It states that the gaps between primes in the set of