Phi.
The number 1.618 is a wonderful number with its deep relevance to nature. The fibonacci series...
1 1 2 3 5 8 13 21 34.... (a no. is the sum of the last two nos.) also has a relation with 1.618 .
The quotient of two continuous nos. in fibonacci series tends to 1.618! Also the ratio of ones height to the height of one's naval is 1.618. And so is the ratio of male bees and female bees in a bee-hive.
Dan Brown's "The Da Vinci Code" is filled with very intresting facts, apart from confuting the Holy Bible.