Perl has an exponentiation operator (**, just like Fortran's ;-)), so x**n is easy. I believe, however, that Perl uses the C math library's pow routine (and 0**0 is undefined, and should return NaN, regardless of Perl's behavior, but I digress). In any case, writing a sub to calculate small integer powers, with little concern for efficiency, is quite easy. The factorials require a routine. Don't make the mistake of writing a recursive routine to calculate factorials; they are easily, and much more efficiently, calculated by a for loop.

Neither piece is particularly difficult. Beware, though, that numerical programming can be quite tricky when values get large or small. There is a wealth of information to be had, for example at na net and the Dictionary of Algorithms and Data Structures.