Here are some video's that seem to show how the numbers 3, 6 and 9 are 'secret numbers' that are very important  within the world of Numerology.

Called: The Secret Behind Numbers 369 Tesla Code Is Finally REVEALED! (without music)

12m04s:

Called: WHY STUDY MATHEMATICS - Vortex Math part 1 and 2

6m49s:

Weird maths. Talks about the number 3, 6 and 9 at 4m40s:

Called: The Secret Behind Numbers 3, 6, 9 Tesla Code Is Finally REVEALED! (Extended)

26m53s:

A very in depth look at the numbers 3, 6 and 9.