MPI_Comm_size(3) on Linux
The text 026b557b3c0c, as Debian 13 (Trixie), Debian 12 (Bookworm), Debian 11 (Bullseye), Debian 10 (Buster), Debian 9 (Stretch), Debian 8 (Jessie), Debian 7 (Wheezy) shipped it.
Determines the size of the group associated with a communictor