There is no clear evidence that Nikola Tesla actually said that the numbers 3, 6, and 9 are the key to the universe. However, this quote is often attributed to him, and there are several possible reasons why people have associated Tesla with this idea.
One possible reason is that Tesla was known for his fascination with numbers and patterns, and he often used mathematical principles in his work. He was particularly interested in the idea of resonance, which involves the vibration of objects at specific frequencies. It is possible that Tesla saw some kind of connection between the numbers 3, 6, and 9 and the principles of resonance and vibration.
Another possible reason is that the numbers 3, 6, and 9 have some interesting mathematical properties. For example, if you add up the digits of any multiple of 3, 6, or 9, the result will always be a multiple of 3, 6, or 9. This pattern is sometimes called the "rule of three" or the "law of vibration." Some people believe that this pattern holds some kind of mystical significance, and they may have attributed this belief to Tesla.
It's also possible that the association between Tesla and the numbers 3, 6, and 9 is a result of modern-day conspiracy theories and pseudoscience. There are many websites and social media posts that claim that Tesla had access to secret knowledge about the universe, and that he believed that the numbers 3, 6, and 9 held the key to unlocking this knowledge. However, there is no evidence to support these claims, and they are generally considered to be unfounded.
In summary, while there is no clear evidence that Nikola Tesla actually said that the numbers 3, 6, and 9 are the key to the universe, this quote has become a popular meme and is often associated with his name. The reasons for this association are likely to be a combination of his interest in numbers and patterns, the interesting mathematical properties of these numbers, and modern-day conspiracy theories and pseudoscience.