Paul Erdos, distinguished Hungarian mathematician perished in 1996, was very popular both for the huge scientific production and his nonconformist lifestyle habits: he owned nothing- neither a permanent job, neither a home, nor other material goods- and he lived with his colleagues’ and friends’ hospitality dedicating himself only to Mathematic.
Erdos collaborated with a great amount of colleagues, with who he generously shared his volcanic mathematic intuitions. Being able to work directly with him must have been a thrilling and valuable experience, so as to deserve to quote not only his coauthors, but even his coauthors’ coauthors and so on, and to quantify this concept has been invented the Erdos number.
Chiquadro Informatica has an Erdos number of 4: Paul Erdos, Samuel Zaks, Nicola Santoro, Fabrizio Luccio, Angelo Gregori.