Erdos Number

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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.
A person's Erdös Number, named after the prolific mathematician Paul Erdos, is the length of the shortest chain of co-authored, referred papers from the person to Erdös. It follows then that Erdös' own Erdös number is 0, anyone that has co-authored with Erdös has an Erdös number of 1, and so on. Colin Wright has an Erdös number of 2, having co-authored with Ron Graham, who co-authored with Erdös many times.

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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