ChatGPT says

There are many books written on the I Ching, ranging from academic studies and translations to practical guides and interpretations. It’s difficult to give an exact number as new books continue to be written and published. However, the number of books on the I Ching is likely in the thousands or even tens of thousands. The I Ching has been a subject of interest and study for many scholars and practitioners over the centuries, and its influence can be found in various fields, such as philosophy, religion, psychology, and literature.