There's this concept of an Erdős number for an academic author: take the graph of academic authors where two authors are joined together if they have written a paper together; then your Erdős number is the number of hops from you to the currently deceased mathematician Paul Erdős.
I first read about him a decade ago in The Man Who Loved Only Numbers but I've never got round to actually computing my number 'till now.
Borja Sotomayor shares a co-author with me (Ian Foster), so my number is less than or equal to his. He is number 6, so my number is ≤6, through this chain:
Ben Clifford → Ian T. Foster → Patrick H. Worley → Robert S. Schreiber → John Russell Gilbert → Roger C. Entringer → Paul Erdös
(p.s. its hard to type the ő in Erdős. Its not ö, although it looks like it)