There is a phenomenon that both Chinese and Japanese cherish odd and even numbers.
In the Ancient Jocko period, Chinese people value the number of "two"; the heaven and the earth, the Yin and Yang, they are united as "one." This is called "Yin-Yang-he-yi" in Chinese.
On the other hand, the ancient Japanese value the number of "one", a curving circle. They loved "one" which is still and delicate, that is harmonized from the contrasting "two". This is called "In-you-gou-itsu" in Japanese.