Computers are really good at doing math. “Calculate something” is really not a whole lot of info. Are you calculating a billion recursions or the first 10,000,000 digits of pi? Or are you just doing some kind of basic non-recursive formula?
As mawburn said, this isn’t a whole lot of info to go on.
That said, Python’s numpy may be of interest to you, if you are developing the site in Python.