Answer: 4 trivial factors.
The positive +1 and +N and the negative -1 and -N.
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: 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.
Russell collaborated very little and no Erdös number can be found using research articles. But, as pointed out by Sachi Sri Kantha at "the Erdös number project" Russell and Albert Einstein did coauthor the Russell-Einstein "Peace" Manifesto of 1955.