Martin Stacey's Erdős Number: 4
For many years Erdős Numbers have been part of the folklore of mathematics - your Erdős Number is the number of coauthor relationships that link you to the Hungarian mathematician Paul Erdős (1913-1996), who produced a world record 1521 publications over 60 years with a world record 509 coauthors. The Erdős Number Project studies coauthorship relations as a real-life example of a very large graph whose properties can be analysed. My Erdős Number is at most 4, by two separate paths.
Paul Erdős 0 - Robert W. Robinson 1 - Lionel March 2 - Christopher Earl 3 - Martin Stacey 4
Paul Erdős 0 - Brendan D. McKay 1 - Marty J. Wolf 2 - Catherine Flick 3 - Martin Stacey 4
Of my coauthors, Chris Earl and Catherine Flick have an Erdős Number of 3. Several others also have Erdős Numbers of 4 or less: Simisola Akintoye, Alan Blackwell, Laurence Brooks, Larry Bucciarelli, Luke Church, John Clarkson, Claudia Eckert, Damian Eke, Malcolm Fisk, Terry Knight, Tonii Leach, Neil McBride, Sebastian Macmillan, Brendan O'Donovan, Adebowale Owoseni, Helen Sharp, Derek Sleeman, Daniel Whitney, Sara Wilford.
The rest (Erdős Number not more than 5) are: Aladdin Ayesh, Kamal Bechkoum, Rodney Buckland, Jenny Carter. Keh Niang Chee, Peter Edwards, Pam Garthwaite, Kilian Gericke, Neil A.B. Gray, Rafaela Hillerbrand, Timothy Jarratt, Ian Kelly, Kristina Lauche, Yee Mei Lim, Jeanette McFadzean, Chris McMahon, Ahmet Orun, Marian Petre, Michael Poznic, George Rzevski, Li Peng Tan, Victor Taratoukhine, Luke Vella Critien, Jennifer Wiley, David Wyatt.
I'm very grateful to Professor Jerry Grossman of the Department of Mathematics and Statistics at Oakland University, Rochester MI, for supplying the full path from Paul Erdős to Herbert Simon (EN 3, plus 2 more to me). Jerry Grossman manages the Erdős Number Project website, which inter alia lists lots of famous people with low Erdős Numbers.