73 is Sheldon Cooper's favorite number in The Big Bang Theory. He first expresses his love for it in "The Alien Parasite Hypothesis".
Jim Parsons was born in the year 1973. "The Alien Parasite Hypothesis" is the 73rd episode of The Big Bang Theory.
- Sheldon: "The best number is 73. Why? 73 is the 21st prime number. Its mirror, 37, is the 12th and its mirror, 21, is the product of multiplying 7 and 3... and in binary 73 is a palindrome, 1001001, which backwards is 1001001."
- Sheldon: "Chuck Norris wishes... all Chuck Norris backwards gets you is Sirron Kcuhc!"'