Call the prime numbers, in order, p1, p2, p3 and so on. Thus p1 = 2, p2 = 3, p3 = 5, ...
(ii) Explain why p1p2p3 ... pn +1 is either prime or has a prime factor greater than pn for all positive integers of n.
(iii) How does that allow you to prove that there is an infinite number of prime numbers?