Answer: Femur More information: The Femur is not only the longest bone in the human body, it is also the strongest bone. The Femur bone is located in the thigh.

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: 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".