Sheldon wearing a 73 shirt at The Cheesecake Factory.
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.

Subsequently he often wears a t-shirt with the number 73 on it.

Quotes

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."
Leonard: "73 is the Chuck Norris of numbers!"
Sheldon: "Chuck Norris wishes... all Chuck Norris backwards gets you is Sirron Kcuhc!"' 

Lolz!!!!
Now guys, what is your most favorite number

http://bigbangtheory.wikia.com/wiki/73

Five (5)

Big bang theory fan?

Where have you guys been since all time?

My favorite number is 666.

it's a palindrome, it's the 36th triangular number, the number 36 itself is ALSO a triangular number, and it's also square.

666 also equal to the sum of its digits plus the cubes of its digits:

666 = 6 + 6 + 6 + 6³ + 6³ + 6³.

it's also the sum of the squares of the first 7 primes.

666 = 2² + 3² + 5² + 7² + 11² + 13² + 17²

the sum of the first 666 primes contains 666.

666 is also a smith number

last but not the least,

if you start with Alphabets and the number which denotes the position of the number in the triangular number series,
i.e


A = 36
B = 37
C = 38

and so on,


The sum of the letters in the word SUPERSTITIOUS will equal 666.


Sheldon can suck on 73.

franklinjoseph:
Five (5)

Tell us why

Teempakguy:
Big bang theory fan?

Where have you guys been since all time?

My favorite number is 666.

it's a palindrome, it's the 36th triangular number, the number 36 itself is ALSO a triangular number, and it's also square.

666 also equal to the sum of its digits plus the cubes of its digits:

666 = 6 + 6 + 6 + 6³ + 6³ + 6³.

it's also the sum of the squares of the first 7 primes.

666 = 2² + 3² + 5² + 7² + 11² + 13² + 17²

the sum of the first 666 primes contains 666.

666 is also a smith number

last but not the least,

if you start with Alphabets and the number which denotes the position of the number in the triangular number series,
i.e


A = 36
B = 37
C = 38

and so on,


The sum of the letters in the word SUPERSTITIOUS will equal 666.


Sheldon can suck on 73.

Yes, a Big fan of the Big Bang Theory I am.
Quiet a number of reasons y've got there. Meanwhile, the number 666 is revealed 2 be antichristian.

Seven(7)

*A N T H O N Y = 7

*The Number Is D Most Dynamic Odd Number I've Seen; Not Easily Used For Calculation