‘PRIMES AND FACTORS’ 63 directly derived from the series of natural numbers (that is, the series of consecutive integers I, 2, 3, 4, etc.). Each odd number can in fact be built up from two consecutive natural numbers, whereas even numbers cannot. Every odd number, other than 1 itself, is clearly one greater than an even number and is therefore of the form on 1. This is the same as n+4-(n+1) and is therefore the sum of two consecutive natural numbers. No even number can be formed in the same way since, for any pair of natural numbers, one must be odd and the other even so that their sum must also be odd. R B g K g B - & 2 RO it safittial KA TR BEREILA