You are asking for "the" function, but as Tigran notes in the comments there are many many many functions that will give you those 6 values (and then differ from each other when you put in a different $x$). The only way to make progress is to know something about the type of function you are looking for. So let's go back to the beginning.
First of all, you say you have a pair of values, but you don't - you have six pairs of values. Then you say "i.e.," but I don't think you mean that. Do you mean "namely," which I would take to mean that you actually have those six pairs of values and you want a function to fit them? or do you mean "e.g.," which I would interpret to mean you are making up those six pairs and you don't have any reason to think there is a simple rule to fit them?
If it's the latter, you are out of luck. Tigran's comment applies, and the value corresponding to, say, $x=10,000,000$, could just as easily be 1,000 as $\pi$ or $-\sqrt2$ or $49867584932/409685753421$ or anything else you care to name.
So we come back to the question, do you have a reason to expect some particular kind of function is involved? If, for example, you have some reason to think there's a polynomial going on here, then Giuseppe's comment is spot on; look up Lagrange interpolation. But your values are growing too slowly for a low degree polynomial to be a likely explanation. So, again, where do those six pairs come from?