The number 73 is a fascinating figure that holds a unique and celebrated status across mathematics, science, and popular culture. It’s far more than just a prime number; it’s a number with personality.
Here’s a deep dive into the significance of the number 73.
- The “Superstar” Prime Number
In the world of mathematics, 73 is revered for its exceptional properties, especially as a prime number.
· The 21st Prime Number: It is the 21st prime number in sequence (2, 3, 5, 7, 11, … 71, 73).
· Mirror Prime: Its mirror, 37, is also a prime number (the 12th prime).
· Mirror Property: Even more remarkably, its mirror index numbers are also mirrors of each other: 73 is the 21st prime, and 37 is the 12th prime.
· Binary Palindrome: 73 in binary is 1001001, which reads the same forwards and backwards. This makes it a palindrome in the base-2 number system.
· Sum of Digits: 7 + 3 = 10, which is a base-10 number.
· Product of Digits: 7 x 3 = 21, which is not only the index of 73 as a prime but also its mirror (37 is the 12th).
· Sheldon Prime: This collection of “mirror” and “product” properties is so unique that mathematicians have dubbed 73 the “Sheldon Prime” after the fictional physicist Sheldon Cooper from The Big Bang Theory, who famously explained its perfection.
- The Big Bang Theory & Pop Culture Icon
The number 73 was catapulted into pop culture stardom by the hit TV show The Big Bang Theory.
· Sheldon’s Favorite Number: In the show’s 73rd episode, titled “The Alien Parasite Hypothesis,” Sheldon explains why 73 is the best number.
“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.”
· T-Shirt Legacy: Sheldon’s obsession is so well-known that “73” appears on merchandise, and the actor Jim Parsons (who played Sheldon) often saw fans holding up “73” signs at conventions.
· The Ultimate Nod: The show’s final episode paid homage to this running gag. In the series finale, the apartment elevator, which was broken for the entire 12-season run, is finally fixed. The repairman’s badge number is #73.
- In Science and Technology
· Atomic Number of Tantalum: On the periodic table, the element Tantalum (Ta) has the atomic number 73. This rare, hard, blue-gray transition metal is highly corrosion-resistant and is used in electronics, particularly for capacitors in mobile phones and computers.
· Amateur Radio: In Morse code, “73” is a traditional amateur radio sign-off meaning “best regards” or “goodbye,” similar to “sincerely” in a letter. Its origin is somewhat murky but dates back to the 19th-century Phillips Code, where it was one of many numerical abbreviations to save time on early telegraph systems.
- Other Interesting Appearances
· The Year 73 AD: A significant year in history, it was the final year of the famous Siege of Masada, where Jewish Sicarii rebels made their last stand against the Roman Empire.
· Sports: It’s a common jersey number in various sports, most famously worn by American football Hall of Fame offensive lineman John Hannah with the New England Patriots. Larry Allen, another NFL great, also wore it.
· NASA’s Space Shuttle: The final flight of the Space Shuttle program was STS-135. If you add the numbers (1+3+5) you get 9. Its predecessor was STS-134 (1+3+4=8). Before that was STS-133 (1+3+3=7), and before that was STS-132 (1+3+2=6). The mission before that, STS-131, adds up to 5. Following this pattern backwards, you eventually land on the number 73.
Conclusion
The number 73 is a true rarity: a number that is objectively interesting based on its mathematical properties and subjectively beloved due to its cultural impact. It bridges the gap between the abstract beauty of mathematics and the relatable world of storytelling, making it, in the eyes of many, the perfect number.