3-6-9 though often associated with Tesla, the three numbers are also associated with Pythagoras.

As far as 666 - numbers from the Bible supposedly are meant to engender fear - something I personally reject. As far as numerologically speaking I see your on a good track. Try checking out numerology as related to the Major Arcana of the Tarot. (see Angeles Arrien - Handbook of The Tarot)

In Gurdjieff's use of the triad 3-6-9; it is a part of the Enneagram as a process tool of completion: https://medium.com/my-unpopular-opinion/dynamics-of-completion-8a09b318a130