If you coauthored a paper with Erd\H{o}s, your Erd\H{o}s number is 1. If you coauthored a paper with someone whose Erd\H{o}s number is $n$, then your Erd\H{o}s number is (at most) $n+1$. For more information about Erd\H{o}s numbers, see http://www.acs.oakland.edu/$\sim$grossman/erdoshp.html My link with Erd\H{o}s is through Jogesh Babu, Statistics, Penn State who wrote several papers with Erd\H{o}s.