The result is mathematically correct, but the display could be simplified. 1301357606610903 / 4722366482869645213696 equals 1 / 3628800. Now it matters, what exactly your question is. Do you want to know how to simplify the output or why the values are displayed in this way?
Move the factorial out of the symbolic part to the numerical part:
FuncApprox = FuncApprox + f_derrived(a) * (x - a)^i / factorial(i)
This works also, when i! exceeds flintmax.
[EDITED] Another solution:
FuncApprox = FuncApprox + (f_derrived(a) / factorial(sym(i))) * (x - a)^i;
Best Answer