Naturally, a simple Google search will find correlations between those numbers and their significance in the universe. Likely it's going to have to do with things like numerology and sacred geometry. But the idea that the universe and everything in it is mathematical is also a theory that physicists like M.I.T. professor Max Tegmark consider plausible.
According to Scientific American, in his book, "Our Mathematical Universe" Tegmark argued, "our universe isn't just described by math, but that it is math in the sense that we're all parts of a giant mathematical object, which in turn is part of a multiverse so huge that it makes the other multiverses debated in recent years seem puny in comparison."
So, there is that simple, headache inducing answer, but Tesla was not a mathematician. However, he was concerned with energy and magnetic fields, and his mind was somewhat of an anomaly, so it's intriguing to think he had some sort of cosmic insight. The American Association for the Advancement of Science reported that he had an eidetic memory, creating groundbreaking inventions from his mind without even sketching them out. He is said to have had "blinding" visions in which he would get ideas for his inventions. His proclamation about the numbers 3,6, and 9 may have come from such a vision.
