> 50% of integers are have a factor under 3
every other number is divisible by 2, that is literally half.
> 73% - under 6
Well I think about it this way: every other number is divisible by two, every third number is divisible by 3 and every fifth number is divisible by 5. It just so happens that some of the numbers that are divisible by 2 are also divisible by 3 or 5 such as 10 for instance. Thus the 73% is nor rly surprising.
1/2 + 1/3rd of what remains + 1/5 of what remains - the intersections!
> but then it slows down to a trickle. 88% under 100, and just 92% under 1000.
I honestly expected it to be a bit lower than 92 but I am clearly wrong about this. Here is an interesting quick visualization I made. Blue are primes, whites are composites!
Edit: you can clearly notice a diagonal shape in the pic above. If you however change the table from 5 cols to any N cols, you will get a distinct shape for each N. It's pretty cool to play with actually. There are a ton of shapes that have been known and used for centuries. I'd highly recommend googling around and reading a bit about them on wikipedia!