Play this article
sudo lsof -PiTCP -sTCP:LISTEN
will get an answer like this
..
Dropbox 684 user 82u IPv4 0xXXXX 0t0 TCP *:17500 (LISTEN)
Dropbox 684 user 83u IPv6 0xXXXX 0t0 TCP *:17500 (LISTEN)
Dropbox 684 user 122u IPv4 0xXXXX 0t0 TCP localhost:17600 (LISTEN)
Dropbox 684 user 125u IPv4 0xXXXX 0t0 TCP localhost:17603 (LISTEN)
...