PARI/GP is a formal calculation system developed since 1983 for use by number theory researchers. It is now used all over the world by three main groups, namely professional mathematicians, students and amateurs with a passion for the distribution of prime numbers or the decimals of famous constants. PARI/GP has been cited in 1029 research articles and has been regularly cited since 2010 (< 30) with the rate rising since 2018 (> 45). The system is used by almost all number theorists worldwide, with an estimated user community of 25,000 people who can take part in regular week-long workshops including hacking sessions to facilitate the inclusion of new contributors.