73

Observation
Sheldon Cooper:


 * $73$ is the best number:


 * $73$ is the $21$st prime number.


 * Its mirror $37$ is the $12$th prime number.


 * Its mirror $21$ is the product of multiplying, hang on to your hats, $7$ by $3$.

Leonard Hofstadter:


 * So $73$ is the Chuck Norris of numbers!

Sheldon Cooper:


 * Chuck Norris wishes.


 * In binary, $73$ is a palindrome: $1001001$, which is the same backwards as forwards.


 * All Chuck Norris gets you backwards is Sirron Kcuhc!