Answer: 3 Octopuses have three hearts; two branchial hearts that pump blood through each of the gills. The third heart is a systemic heart that pumps blood through the whole body.
Answer: A perfect number. 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".
