Earlier quoted context omitted.
To be fair in many parts of the world 40000 and 100000 is written like this 40.000 and 100.000. So it may confuse non Americans.
Yes, I don't really use thousands separators because I use both number systems regularly and the ambiguity annoys me. It's not a practical issue in this case I think as almost everyone would assume US numbers here. But they feel weird to me somehow. I have used spaces at times as a thousands separator, but that might be even more confusing.
For the decimal marker "." and "," are both acceptable. Use whichever is appropriate for your country or for where you readers are or whatever.
Unicode U+2009 (thin space) or U+202F (narrow no-break space) are good for this, but unfortunately neither of them are among the Unicode that works on HN. HN converts them on input to a normal space.
E.g., 12 345 (space), 12 345 (U+2009), and 12 345 (U+202F) are all the same on HN.
That wasn't always the case. I'm not sure when they started filtering these out on input, but 6 years ago I posted a comment where I pasted in some text demonstrating various Unicode spaces [1], and that works so the change was sometime in the last 6 years.
Note: it only works for me in Chrome. In Firefox and Safari the browser changes them all to normal space. I don't know if that is just something peculiar to my Firefox and Safari installations or if Chrome just does Unicode better than they do.