Answer: Paul Erdős
Erdős published at least 1,525 mathematical papers during his lifetime. He engaged more than 500 collaborators and devoted most of his time to mathematics up until his death in 1996 at the age of 83 years old.
Portman collaborated (using her birth name, Natalie Hershlag) with Abigail A. Baird, who has a collaboration path (Gazzaniga, Michael S. -> Victor, Jonathan D.) leading to Joseph Gillis, who has an Erdős number of 1.
Of course, as time passes, the smallest Erdős number that can still be achieved will necessarily increase, as mathematicians with low Erdős numbers die and become unavailable for collaboration.
Answer: 4 trivial factors.
The positive +1 and +N and the negative -1 and -N.
Answer: Pierre-Simon Laplace has an Erdős number of at most 14!
According to "The Erdös number project" a path to Laplace was found by Leonid Yanushevich giving the famous mathematician an Erdös number of at most 14.
Answer: Paul Erdős, of course!
As the Erdős number describes the "collaborative distance" in authorship of mathematical papers between mathematician Paul Erdős and another person it is only natural that Paul Erdős holds this position.