11 Things You Probably Haven't Spotted On The Big Bang Theory

73 is Sheldon's favorite number, 1973 is the year actor Jim Parsons was born AND Sheldon expresses his love for his beloved digits in the sitcom's 73rd episode, gushing: "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."

In series three episode The Pants Alternative, Sheldon wakes up the morning after the night before to watch his drunken antics posted on YouTube. What you might not have noticed is Sheldon's username: "ob1" in homage to Star Wars character Obi-Wan Kenobi.

Series six episode The Holographic Excitation sees Sheldon and Amy discuss what to dress up as on Halloween. One of the suggestions on Amy's list is Blossom and Joey – the 90s sitcom that actress Mayim Bialik starred in as Blossom Russo. Dharma and Gregg were also on the list – characters created by Big Bang's showrunner Chuck Lorre.

It's not the first time Blossom has been mentioned on the show. Back in series one episode The Bat Jar Conjecture, Raj suggested possible replacements for Sheldon on the physics bowls team, naming "the actress who played TV's Blossom" because "she's got a PhD in neuroscience or something." Bialik has a PhD in real life and went on to join the show in its third series.

They're all of actress Kaley Cuoco posing with members of the Big Bang Theory cast and crew.

Season three episode The Excelsior Acquisition saw a guest spot from Marvel veteran Stan Lee. But what you might not have noticed is the judge who Sheldon faces in court (for running a red light) is called J. Kirby – a nod to Lee's contemporary, comic book writer and editor Jack "The King" Kirby.

Wil Wheaton has appeared in many Big Bang Theory episodes, but season six installment The Habitation Configuration features a glimpse of the front of his fictional home. The house number? 1701 – a reference to his role on Star Trek: the Next Generation where the USS Enterprise's registry number was NCC-1701-D.

Meanwhile, Amy's apartment number is 314. For those of you who didn't pay attention in maths lessons, that's a reference to the mathematical constant Pi (π) which is 3.14 (to two decimal places).

If you keep a close eye on season four episode The Raiders Minimization, you'll see an equation scrawled on a whiteboard. Now, it's no news to fans that all equations featured on the show are authenticated by David Saltzberg, but the physicist was nervous about this particular entry as it didn't quite add up. That's because the whiteboard was commandeered by executive producer Steve Molaro. He stole the equation from...

If you compare the two equations, you'll notice they're identical. The only problem is, the Indiana Jones film doesn't appear to have had a science consultant as, according to Saltzberg, it "makes no sense".

Sheldon often wears t-shirts of The Flash, but have you spotted the Big Bang Theory-themed clothing sported by Cisco Ramon in The CW's adaptation?