73

73 is Sheldon Cooper's favourite number in The Big Bang Theory.

Quotes

 * Sheldon: "The best number is 73. Why? 73 is the 21st prime number. It's mirror, 37, is the 12th and it's mirror, 21, is the product of multiplying 7 and 3... and in binary 73 is a palindrome, 1001001, which backwards is 1001001."


 * Leonard: "73 is the Chuck Norris of numbers!"


 * Sheldon: "Chuck Norris wishes... all Chuck Norris backwards gets you is Sirron Kcuhc!"