Простите за невежество, а что есть "первый тип" и "второй тип"?

http://personalwebs.oakland.edu/~grossman/compute.html

Finally, there is the issue of which kind of Erdös number to use. Our data are for Erdös numbers of the first kind, where a paper with k authors gives rise to C(k,2) edges. (For example, if Tom, Dick, and Harry wrote a joint paper, then there are edges from Tom to Dick, from Dick to Harry, and from Harry to Tom.) Purists would insist that only papers with two authors should count. It might be a bit harder to compute these Erdös numbers of the second kind by hand. Our program for automated searching will find both kinds, however, so feel free to write and ask.

Спасибо! :)