Erdos Number 


There is also a Bacon number, which goes via films and starts at (or ends at) Keven Bacon, and there is a Sabbath number, which goes via musical collaborations back to the group Black Sabbath. Colin has a Bacon number of at most 4, depending on what you count, and as yet does not have a finite Sabbath number, although he is working on both. 
There is also an Erdös Number of the second type, in which only papers with exactly two authors count. This is much more restrictive. Colin's Erdös Number of the second type is three, going via Graham Brightwell, thence Bela Bollobas and Paul Erdos.
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Quotation from Tim BernersLee 