Nth term of a series

Hi,i am working on a c++ project which will find the nth term of a given series.The series would be given in the form of first 4 or 5 terms.I have the basic alogorithm which can find the nth term of a polynomial series given initial terms.The problem being tht the number of initial terms required is proportional to order of the series.So,as the order of polynomial series increases ,we need more number of initial terms.
I shall oblidge if anybody can provide me with a better algorithm or any other way to find the nth term of the series given only 4 or 5 initial terms!!

re: Nth term of a series

I'm sorry, that can't be done: for a polynomial of degree n you need at least n+1
discrete (x,y) samples to completely describe the polynomial. And then there
are the exponential or transcedental functions that connot be described by any
finite degree polynomial at all.

kind regards,

Jos