The recent question about the most prolific collaboration interested me. How about this question in the opposite direction, then: can anyone beat, amongst contemporary mathematicians, the example of Christopher Hooley, who has written 91 papers and has yet to coauthor a single one (at least if one discounts an obituary written in 1986)?

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 


How about Marina Ratner. I believe she has had no collaborators. 


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/textidx?c=umhistmath&idno=AAN8909 


Leopold Vietoris (18912002) wrote more than 70 papers, only one of them with a coauthor see here. 


I always like William Veech (57 papers) although it's unlikely, he will catch up. But his citation count is higher (after mathscinet). 


I think amongst the Field medal laureates, Atle Selberg would be a good candidate: He wrote 48 articles, and only one is a collaboration (with S. Chowla), see this link. 


Here is what Zentralblatt (which now includes Jahrbuch der Mathematik) says about Godeaux, Lucien. https://zbmath.org/authors/?s=0&c=100&q=Godeaux%2C+L AuthorID: godeaux.lucien Published as: Godeaux, L.; Godeaux, Lucien Documents indexed: 1213 Publications since 1906, including 28 Books CoAuthors 1 Brocard, H. 1 Errera, Alfred 1 Mineur, Adolphe 1 Plakhowo, N. 1 Rozet, Octave And about Vietoris, Leopold AuthorID: vietoris.leopold Published as: Vietoris, Leopold; Vietoris, L. Documents indexed: 80 Publications since 1916, including 1 Book CoAuthors 1 Tietze, Heinrich 


I have just noticed that MathSciNet lists a total of 81 publications for John H. E. Cohn: among them, there is only one paper written jointly (viz.: J. H. E. Cohn; L. J. Mordell, On sums of four cubes of polynomials. J. London Math. Soc. (2) 5 (1972), 74–78.). Fibonaccinumbers enthusiasts will surely recognize the name because it was J. H. E. Cohn the individual who proved around 1964 that the largest perfect square in the Fibonacci sequence is $F_{12}=144=12^{2}$; Y. Bugeaud, M. Mignotte, and S. Siksek would establish some fourtyodd years laters that, in point of fact, the only non trivial perfect powers in the Fibonacci sequence are $F_{6}=8=2^{3}$ and $F_{12}=144=12^{2}$. 

