Write a recursive rule for all positive odd numbers.

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 number if 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 number if a is an odd number, a + 2 is also an odd number.