Tesla’s 369 obsession was visible in many aspects of his everyday routine. Walking around the block three times before entering the building, choosing only rooms with numbers which are divisible with the number three, cleaning his dishes with 18napkins, also a number divisible with 3,6 and 9…everything had to be in some way related to those numbers. OCD, germophobia, it all might have to do something with it, but allegedly the famous physicist said: “If you only knew the magnificence of the 3, 6, and 9, then you would have a key to the universe.” If you find a perspective from the mathematical side, a digital root that equals nine can be found in lots of shapes and vectors in space. Speed of light, the diameter of the Sun, the diameter of the Earth, the diameter of the Moon, seconds in a day, seconds in a week, month, year, minutes also, and so on… it proves that the number nine is present everywhere. How long does the pregnancy last? Nikola Tesla’s 369 key to the universe does not look so abstract when you consider mathematics perspective.