Space in sky between celestial bodies seems is: nothing, Zero. Zero is a huge whole nothing. The biggest whole the humanity could see over his heads. :) see this: 1, 1, 1, 1. There is 4 of 1. They could be written like: (1, 1) (1, 1) - those are pairs. Let's see this: 1, 1, 1. There is 3 of 1. It could be written like (1,1) (1, ) - seems like we have remainder. What then about zero? It has no paired elements, that others even could form. Zero also, hasn't remainder. That mean:
Zero not odd and zero not even! Evrica :)
If whole result of division by 2 not zero and has no remainder, the number is even.