Answer: A perfect number.
More information: You might also think of a perfect number as a number that is half the sum of all of its positive divisors, including itself! This definition is at least 2300 years old as it appears in Euclid's "Elements".
Answer: Paul Erdős, of course!
More information: 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.
Answer: 180 degrees
More information: The angles of a triangle always sum to 180 degrees.
Answer: Pierre-Simon Laplace has an Erdős number of at most 14!
More information: 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: 4 trivial factors.
More information: The positive +1 and +N and the negative -1 and -N.
More information: 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.