Software

Some computer languages, like Ruby, support multi precision numbers out of the box, some need a special function, like Java does, and some require an additional external library like C does. There are also mathematical software environments that have functions to deal with prime calculations, for example Pari/GP. Finally there are prime-specific softwares such as Prime95. There are factoring specific softwares too.

Pari/GP is a free software that has a rich set of functions including many to do with primes such as $forprime()$, $fordiv()$, $isprime()$ and $factor()$ to mention a few. It is also possible to use PARI as a C Language library.

Gnu Multiple Precision (GMP) is a C language library maintained by volunteers. It is fast having a few basic functions.

GWNUM is the C language library that is behind the softwares that find the current largest primes. It is part of the source code to the Mersenne prime search's Prime95 software download.

Prime95 is chiefly used to factor and LL test Mersenne primes. PFGW and LLR are swiss army knife prime hunting programs which are able to prove some numbers prime.

Primo and the software CM are mutlithreaded ECPP programs used to prove a large number prime or not.