The Jon Skeet number is the Erdos Number of Stack Overflow. The above input box only does exact text matching, so make sure you type your display name correctly. There is also a list of all useres with a Jon Skeet number.
The Erdos Number is based on authorship of papers. To calculate a Jon Skeet number I define the "authorship" of answers. First, only questions that are not closed and not community wiki are considered. A question must also have an answer of at least 5 upvotes (doesn't matter if there is an accepted answer or not). The "authors" that answered that question are determined as follows. Say the top answer has X points. All users with an answer in the range [ceil(0.75*X), X] are considered authors.