I have learnt the use of even numbers for font sizes, spacings. The 8 point rule. But still not being able to figure out why Apple still uses odd number for font sizes, spacings and paddings.
Fun fact, humans love odd numbers (<-- UX Collective article). Think about it, 7 wonders of the world, trinity in everything we can define. I've always found this to be a fun detail about humans.
I couldn't find the original article that taught me this (probably, QuickSprout's Complete Guide on the Psychology of a Consumer), but I can't dig that up right now. UX Collective's article will do, the results are the same.