Num.4 (Please help me out)

Consider the set of positive even numbers: 2, 4, 6, 8, …. each next is equal to the previous plus 2. relation of this type is called a recurrence relation. the set of positive even numbers is defined recursively in the following way: 2 is an even numberif a is an even number, a + 2 is also an even number.            example 2:   consider the set of positive odd numbers 1, 3, 5, 7, 9, … each next is equal to the previous plus 2.the set of positive odd numbers is defined recursively in the following way: 1 is an odd numberif a is an odd number, a + 2 is also an odd number.