The Erdo""s Number

Most practicing mathematicians are familiar with the definition of one’s
Erdo""s number [that is actually a long Hungarian umlaut over the “o” but we
will represent it here by the ordinary two-dot umlaut widely available in
html, since the true Hungarian umlaut isn't visible in some browswers — here
is what it looks like if your browser supports it: Erdo""s.]. Paul Erdo""s (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. His Erdo""s number is
0. Erdo""s’s co-authors have Erdo""s number 1. People other than Erdo""s who
have written a joint paper with someone with Erdo""s number 1 but not with
Erdo""s have Erdo""s number 2, and so on. If there is no chain of
co-authorships connecting someone with Erdo""s, then that person’s Erdo""s
number is said to be infinite.


Paul Erdo""s
Born: 26 March 1913 in Budapest, Hungary
Died: 20 Sept 1996 in Warsaw, Poland

Paul Erdo""s came from a Jewish family (the original family name being
Engla""nder) although neither of his parents observed the Jewish religion.
Paul's father Lajos and his mother Anna had two daughters, aged three and
five, who died of scarlet fever just days before Paul was born. This
naturally had the effect making Lajos and Anna extremely protective of Paul.
He would be introduced to mathematics by his parents, themselves both
teachers of mathematics.
.......

Reference:
http://www.oakland.edu/enp/
http://www-gap.dcs.st-and.ac.uk/~history/Mathematicians/Erdos.html