“Even” numbers are evenly divisible by two.
“Round” numbers, in the common sense, are a bit more vaguely defined, but can often be understood to mean something like, “divisible by a power of ten no more than two orders of magnitude less than themselves.”
Are there short words that can be used to describe sets of numbers with other common factors? Is there a word to mean, e.g., “divisible by three”?
threeven.
(Sorry, I couldn’t resist. No, I don’t know of one that’s more universally understood.)
I can’t think of any.
Remember that a lot of our math and counting words evolved in a time when people couldn’t do math. The words “two” and “half” are unrelated to each other, but “three” and “third”, “four” and “fourth” etc. are all clearly related.
If “half” is the only fraction you understand, then “even” is a significant concept. Once people were educated enough to understand division and fractions, they could derive their own words for it and thus “multiple of three” was good enough.
Well, “trisectable,” while not exactly a common word (and not used in this context, when it is used), would pretty much fit the bill. It does, however, lack any connotation of the three integral equal parts.
Perhaps “modulo” fits the bill? It’s not that much shorter than saying “divisible by” but you can say, for example, 7=5 (mod 2) or (7 mod 3) = (10 mod 3). There aren’t really any easy ways to express divisibility without resorting to math symbols anyway.
Ooh, thanks, Jurph! I just saw the term “modulo” in a recent Staff Report but didn’t think to investigate further. Maybe there are some modular math terms that I can use.
Evenly divisible by three. If you want to be fancy, you can say congruent to 0 mod 3.
But that’s four words. OP was looking for one. 
And had already provided a three-word solution. 
But, in case it was ultrafilter’s point to the OP, it’s worth asking: Why do you want a single word? Idle curiosity or do you actually think there is something you can do with one word for this which you can’t do with one short phrase? Because, you know, there isn’t.
Tripartite will do.
Thirdable. Sure, you can argue that 4 is thirdable, because 1 1/3 is one third of four, but if there were four apples, and three of us, how ya gunna third 'em?
Exactly.
Multiple of three? Not one word, but can be easily modified for any number.
Not really, no. Tripartite just means mde up of three parts. Period. They don’t have to be equal or even congruent parts so it wouldn’t necessarily fit the concept the OP is looking to express.
I think you are misunderstanding the meaning of even versus odd/uneven.
Even/odd only pertain to a numbers relationship to two.
Even means exactly divisible by two, whereas odd/uneven means not exactly divisible by two.
That’s it!
I suppose you could argue integer means exactly divisible by one, but odd doesn’t.
Why three , what about four, five six, …etc. There aren’t single words to describe numbers that are exactly devisible by these either.
I would assume the reason why there is no single word is that there really hasn’t been a necessity or as we can see in this thread, a consensus on what that word should be.
I would assume that, from a mathematical standpoint, “even” is a more interesting property than “evenly divisible by three.” Even + even = even, even + odd = odd, odd + odd = even. Tripart + tripart = tripart, but not necessarily odd or even.
It’s also easy to look at a number of any length and know if it is odd or even — check the last digit — not so much with threes. It’s strange that we don’t have divisible-by words for “by fives” and “by tens” which are just as easy to recognize as evens. It suggests the idea of “evens” and “odds” arose with the idea of sharing, possibly far predating the base-10 number system.
I submit since “divide” derives from Latin meaning “to separate in two” the words trivide and trivisible might do.
Not one single person in this thread is misunderstanding this; not even the OP.
Harder than simply looking at the last digit, but still not terribly difficult: Add up the digits that form the base-10 representation. If that sum is divisible by three, so is the original number. Apply recursively if needed.
The word you need is ‘thridding’.
Look it up, yes, there truly is such a word, even if it is almost obsolete in the rest of the English speakng world except Yorkshire (there may be more use of it in Scandinavian related nations), and it is the antecedant word for ‘riding’, it is also, unsurprisingly, the antecedant word for ‘third’.
Riding is the word used to describe any one of the three county parts of Yorkshire - England, hence East Riding of Yorkshire, West Riding, and… well you get the picture.
http://www.northeastengland.talktalk.net/About_Yorkshire.htm