Looks like some sort of Taylor/Maclaurin series.
Let's see:
The sum if i=0 and n=1 is e^x
i=1, n=1: e^x - 1
i=0, n=2: cos(x)
i=1, n=2: sin(x)
i=2, n=2: cos(x) - 1
After that I'm not sure.
And then you have to sum from i=0 to n, so for n=0, f(x) would be undefined for x=0, and infinity for everything else. For n=1, f(x) would be 2*e^x - 1, and for n=2 f(x) would be 2*cos(x) + sin(x) - 1. Not really sure what the point of that is...
What language is that? It took me forever just to figure out what it was saying...
On an unrelated note, you should become active on #curlybrace >_>
EDIT: crap no I was mistaken about the sin/cos thing, I think maybe it's supposed to be sinh and cosh instead? M'eh, I'm not sure, don't quote me on that.
EDIT: yes, it is indeed supposed to be sinh and cosh. You can quote me now if you really want to
