An odd number is an integer that is not divisible by 2. The mathematical expression is 2k+ 1. Odds can be divided into positive odd numbers and negative odd numbers.

Among integers, numbers that are not divisible by 2 are called odd numbers. In daily life, people usually call positive odd numbers singular, as opposed to even numbers. Odd numbers can be divided into positive and negative odd numbers. The mathematical expression of odd numbers is:

Positive odd numbers: 1, 3, 5, 7, 9,1,13, 15, 17, 19, 2/kloc-.

Negative odd numbers:-1, -3, -5, -7, -9,-1,-13,-15,-17,-/kloc.