1. Adjacent number is a mathematical term, which means that in the natural numbers arranged from small to large, two adjacent numbers before and after a number are adjacent numbers of the number.

2. For example, if 1 has adjacent digits, the preceding adjacent digit is 0 and the following adjacent digit is 2, then the adjacent digits of 1 are 0 and 2. For example, 5, if the front neighbor is 4 and the back neighbor is 6, then the neighboring numbers of 5 are 4 and 6.