Mathematician Paul Erdos is so well known in his field that other academics often refer to their "Erdos number," which identifies how many degrees removed they are from having worked with him, Eric Barker writes. Erdos' networking secret was his generosity. "He wasn’t a sleazy social climber. And given his eccentricities he was about as far from socially skilled as you can get. He was a giver," Barker writes.