Odd difference means that the difference between two adjacent digits of a positive integer from left to right is odd. You can take the following steps to deal with odd differences: 1. Determine that the number is odd difference, and the number of digits that need to meet this number is odd. At the same time, starting from ten digits, the difference between every two adjacent digits is odd. 2. Mathematical methods can be used to simplify the analysis of odd differences. For example, the odd difference is abcd, which can be expressed as a *103+b *102+c *10+d, satisfying the following formula: (a-b)% 2 = (b-c)% 2 = (c-). For example, some strange mathematical laws and interesting questions can be deduced by using the properties of odd differences, such as "the sum of two odd differences must be even"