PARI/GP is a widely used computer algebra system designed for fast
computations in number theory (factorizations, algebraic number theory,
elliptic curves...), but also contains a large number of other useful functions
to compute with mathematical entities such as matrices, polynomials, power
series, algebraic numbers etc., and a lot of transcendental functions. PARI is
also available as a C library to allow for faster computations.
Originally developed by Henri Cohen and his co-workers (Université Bordeaux I,
France), PARI is now under the GPL and maintained by Karim Belabas with the
help of many volunteer contributors.