Least collaborative mathematician

Lucien Godeaux wrote more than 600 papers and not one of them is a joint paper. He cowrote a textbook in projective geometry. Mathscinet records only 15 citations to all these papers! But there is something called Godeaux surfaces which is mentioned in the literature. This is about the weirdest example I know.

http://www.ams.org/mathscinet/search/author.html?mrauthid=241534

Until well into the 20th century, collaboration was more the exception than the rule among mathematicians. As an example, define the Betti number as the distance to Enrico Betti in the collaboration graph. Well, it seems that your Betti number is infinite (unless you are Enrico Betti): indeed, according to the link below, Betti is an isolated point in the collaboration graph: http://quod.lib.umich.edu/cgi/t/text/text-idx?c=umhistmath&idno=AAN8909

Leopold Vietoris (1891-2002) wrote more than 70 papers, only one of them with a coauthor see here.