Erdös Numbers   

Erdös published papers with more than 250 different co-authors. Because of this prolific number a new term was coined. A person gets an Erdös number of 1 by having published a joint paper with Erdös, an Erdös number of 2 by publishing a joint paper with someone with an Erdös number of 1, and so on. Someone who published multiple papers with Erdös gains a fractional Erdös number; 2 joint papers earns you an Erdös number of 1/2, 8 joint papers earns you an Erdös number of 1/8, and so on.

In 2001, for the first time since 1935, no new co-authors were added to the list of mathematicians with an Erdös number of 1 (or less). The count stands at 507.

The number of mathematicians with an Erdös number of 2 increased by 230, however, to 6127. Erdös numbers range to 15, but the average is less than 5. The median number of papers is 2 and the mean is approximately 7.