number theory-oriented computer algebra system
The PARI system is a package which is capable of doing formal computations on recursive types at high speed; it is primarily aimed at number theorists, but can be used by anybody whose primary need is speed. It is possible to use PARI in two different ways: 1) as a library, which can be called from an upper-level language application (for instance written in C, C++, Pascal or Fortran); 2) as a sophisticated programmable calculator, named gp, which contains most of the control instructions of a standard language like C.
Homepage: https://pari.math.u-bordeaux.fr/