Why aren't there 13, 15, 17, 18 divisions in Japan?

Because after World War I, due to economic problems, Lu Xiangyu was disarmed at that time. At that time, several of the 20 divisions were cut off. 18 division is also listed here. In addition, even the junior military academy at that time was reduced from six to one. With the saved military expenses, two heavy artillery wings, a mountain artillery wing and a tank wing were formed. History is called "Yuheng Disarmament". Later, before the outbreak of the war of aggression against China, the Japanese army rebuilt these divisions in order to expand its military strength.