Six the perfect number
If you are a fan of the Prisoner TV series, asking the question” Why six is a perfect number”, might get you the answer “That would be telling.” However in mathematical terms a perfect number is one where when all the factors (except itself) are multiplied together they equal the number itself AND the factors when added together equal the number.
The factors of six (excluding itself) are 1,2,3:
1*2*3 = 6 AND 1+2+3=6.
Six is the smallest perfect number. The next known perfect numbers are 28, 496, and 8128.