As usual, the hard problem is how you define "Elementary" which is why the posters always show 17, and then you get numbers that go as high as 995.5 (and the .5 is an interesting result as well).

Isn't it just a thing that cannot be broken into / explained as a combination of more elementary things? ie. as far as we know an electron is an elementary particle because it can't be split into smaller components nor is there any evidence that it contains something smaller (unlike, say, an atom or a proton).