I mentioned this in another comment, but Platonism only is concerned with how humans are able to communicate with each other using shared concepts, if the "entities" exist as you say, most people who study philosophy would agree that insofar as they exist, they exist in people's heads (since, something existing in your mind is still real in so far as it has a material reality).
That's not true. In the Philosophy of Mathematics when people refer to Platonism they make two claims. That mathematical objects are 1. abstract and 2. independent. (also this is the case in traditional Platonism).
An object is abstract if it is not spatiotemporal or causal. Asking what the number 4 weighs or does makes no sense. It is not mental, i.e. mind independent, in that it exists outside of any agent's thoughts. A Platonist would argue that even an alien civilization is going to discover, not invent, logic and natural arithmetic. Unlike say, Inglourious Basterds which is a mental product that did not exist before Tarantino thought it up.
It is debatable if that is the case in traditional Platonism, the evidence for artificial forms comes from a single epistle (the 7th) that is arguably fabricated. I've read some of this epistle in the original, and stylistically it is very far removed from Plato's regular style, and the language resembles (to me) Koine Greek and not Attic Greek.
In any case, just because someone calls themselves a platonist doesn't mean they've carefully studied Plato. In the same fashion as Kant, asserting time and space precede the apprehension of objects that are necessarily within time and space does not imply that time and space are necessarily part of the world itself, but only that one's means of judgement begins with the notions of time and space. In the same way, whether or not you agree with Kant, it is entirely plausible to assume instead that there is a shared faculty in the minds of humans that allows us to conceive of things like 4, and addition and subtraction and mathematical functions in general, and this faculty would neither be abstract nor independent but biological and empirically observable. If this latter case is true, then it would prove to be far more useful for scientific investigation than simply assuming that the reason why we can communicate about the number 4 is because it exists abstractly and independently, because that doesn't tell us anything more about why we have shared concepts of numbers in the first place.
