Erdös number

Paul Erdös (1913-1996) was one of the most prolific mathematicians of all time. He authored or coauthored around 1500 articles and books. The Erdös number measures the distance of a given mathematician from Erdös on a graph whose edges denote the relationship of coauthorship (see the Erdös Number Project Home Page for details). My Erdös number is currently 4 via Richard Hall, Hal Smith, and Klaus Schmitt. You can find your collaboration distance with other mathematicians here if you have access to MathSciNet.

Erdös, P., Hall, R. On the values of Euler's Phi-function Acta Arith. (22) (1973) 201-206.

Hall, R., Goldstein, M, Sheil-Small, T., Smith, H. L., Convexity preservation of inverse Euler operators and a problem of S. Miller Bull. London Math. Soc. 14 (1982) no. 6 537-541.

Smith, H. L., Schmitt, K Positive solutions and conjugate points for systems of differential equations Nonlinear Anal. 2 (1978) no. 1 93-105.

Schmitt, K., Jacobsen, J., The Liouville-Bratu-Gelfand problem for radial operators J. Differential Equations184 (2002), no 1, 283-298.