Paul Erdős (1913—1996), the widely-traveled and incredibly prolific Hungarian mathematician of the highest caliber, wrote hundreds of mathematical research papers in many different areas, many in collaboration with others.
Erdős's Erdős number is 0. Erdős's coauthors have Erdős number 1. People other than Erdős who have written a joint paper with someone with Erdős number 1 but not with Erdős have Erdős number 2 (like myself), and so on. If there is no chain of coauthorships connecting someone with Erdős, then that person's Erdős number is said to be infinite.
Stefan Szeider's Erdős Number is 2. He is connected with Erdős via two separate chains of coauthorships of length two.
The first chain is via Carsten Thomassen and the papers:
- M. Fellows, M. Fomin, D. Lokshtanov, F. Rosamond, S. Saurabh, S. Szeider, and C. Thomassen. On the complexity of some colorful problems parameterized by treewidth. Information and Computation, vol. 209, no. 2, pp. 143-153, 2011.
- C. Thomassen, P. Erdős, Y. Alavi, P.J. Malde, and A. Schwenk. Tight bounds on the chromatic sum of a connected graph. J. Graph Theory 13 (1989), no. 3, 353-357.
The second chain is via Noga Alon and the papers:
- N. Alon and P Erdős. An application of graph theory to additive number theory. European J. Combin. 6 (1985), no. 3, 201-203.
- N. Alon, G. Gutin, E.J. Kim, S. Szeider and A. Yeo. Solving MAX-r-SAT Above a Tight Lower Bound. Algorithmica, vol. 61, no. 3, 2011, pp. 638-655.