I was convinced that **42** is a funny number but the last episode of “The Big Bang Theory” (4×10: The Alien Parasite Hypothesis) taught me that **73** is much more fascinating. Far from being addicted to numerology or the strange ideas of Paul Kammerer I just like number games and number theory.

Sheldon Cooper considers **73** being the best number because switching digits, **73** (**21**st prime number) becomes **37** (**12**th prime number). The number **21** includes factors **7** and **3**. Seventy-three in binary (**1001001**) is a palindrome.

The episode aired on December 9th 2010. On December 10th the aforementioned facts were added to the Wikipedia article about 73.

Meanwhile other properties were added (as of December 12th 2010): Of the **7** binary digits representing **73**, there are **3** ones. Also, 37+12=49 (seven squared) and 73+21=94=47*2, 47+2 also being equal to seven squared.

Looking behind the scences, one finds further coincidences: Sheldon’s discussion of **73** appears in the overall **73**th episode of the series and Jim Parsons – the actor portraying Sheldon – was born in 19**73** and, ergo, is now **37** years old (btw: Happy belated Prime Number). Jim was born on 24th of March (month No. 3) and – guess what’s 24 – 3? Right: **21**! And 24 divided by 2? ok – that’s going to become a little boring …

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December 19, 2010 at 5:09 am |

I do agree that 73 is a very interesting number but there is something they misrepresented. 1001001 is not the binary for 73, but the binary representation of 49 which is the hex conversion of 73. Also, while they leave the leading 0 off in its representation, you can’t do that when you flip it. So 01001001 becomes 10010010. So while there are some very interesting facts provided for 73, the show did misrepresent it and Sheldon should have known this. 🙂

December 20, 2010 at 9:25 am |

I do not know in what universe it is common practice to use leading zeros in that way for integers. You are right that the 49 is the hexadecimal representation of 73 but the binary representation of 73 is as simple as: 1*2^6 + 0*2^5 + 0*2^4 + 1*2^3 + 0*2^2 + 0*2^1 + 1*2^0 = 1*64 + 0*32 + 0*16 + 1*8 + 0*4 + 0*2 + 1 = 64 + 0 + 0 + 8 + 0 + 0 + 1 = 73.

P.S.: My date of birth (in the ddmmyyyy convention) is a 8-digit prime number (28121969). Who’s interested may calculate the probability of this coincidence.

January 5, 2011 at 7:20 pm

“I do not know in what universe it is common practice to use leading zeros in that way for integers”

I think the GP was a TI-99/4A programmer at one time and learned binary-dec-hex conversions the way I did- as patterns of two-digit hexadecimal numbers representing one line of an eight-line font-based graphics set (in which you redefinend the font of ASCII characters to get high definition graphics). In 8-bit computer land, where a word is always a byte, yes, the leading zero is normative.

December 24, 2010 at 5:05 pm |

Ummm… exactly why do you have to convert a decimal number into hex before converting it into binary? Sheldon is correct, period. 1001001 in base 2 is precisely 73 in base 10. There’s no reason to use base 16 as an intermediary. That’s something computer programmers do (along with prepending zeros to pad to eight digits), and Sheldon isn’t primarily a computer programmer.

January 4, 2014 at 5:40 pm |

I don’t know where you went to school, but 1001001 is, indeed, the binary (base-2) representation of 73. The far-left “1” is in the 64’s place. The middle “1” is in the 8’s place, and the far-right “1” is in the 1’s place. That means that 1001001 converted to decimal (base-10) is 64+8+1 = 73.

January 11, 2011 at 11:57 pm |

I love The Big Bang Theory an also enjoy little numeracy games an was very pleased to read your findings from the research you have done on the number 73. I will also be boring almost every one I know with your findings so thank you 🙂

January 10, 2012 at 7:49 am |

I also noticed something else:

73 – 10 (7+3) = 63 = 3 X 21

21 = 3X7

63’s digits = 3 X 3

9 X 63 = 567

567 / 7 = 81

81’s digits = 3 X 3

567 / 3 = 189

189 / 7 = 27

27’s digits = 3 X 3

27 X 3 = 81

73 – 3 = 70

70 / (7+3) = 7

81 X 3 = 243

243’s digits = 3 X 3

7 X 7 X 7 = 343

343’s digits = 10 = 3 + 7

May 12, 2013 at 2:40 am |

73+37=110

110=11 x 10

11+10=21

January 18, 2012 at 6:01 pm |

oh wow… I no longer feel like a nerd 😀 I feel like I just watched another episode of The Big Bang Theory.

February 3, 2012 at 12:02 pm |

That is a very kind compliment 🙂

December 20, 2014 at 10:35 am |

I dont mind being called a nerd, if that what takes to watch the big bang theory 😛

March 22, 2012 at 3:55 pm |

It is quite simple if you bring up your Windows calculator, switch to programmer’s calculator and enter 73 in the decimal mode. Then switch to bin format and it will reveal 1001001. Duh. Also, decimal 73 in hex is 49 and 73 in octagonal is 111 another palindrome. To further elucidate but not confuse.

June 25, 2012 at 6:46 am |

well, i must say with numbers you guys rock

and to sheldon cooper, hope he comes with more numbers in the next season

August 9, 2013 at 6:48 am |

There’s another peculiarity: Among the 21 types of vertex where regular polygons meet the one including a polygon with the largest number of edges (42) is 42-7-3. This is a nice combination of 42 and 73 (or of 37 and 42 if you order the polygons as 3-7-42). http://en.wikipedia.org/wiki/Tiling_by_regular_polygons

More about funny numbers: http://blogs.scientificamerican.com/roots-of-unity/2013/08/05/what-is-the-funniest-number/

January 5, 2014 at 4:33 pm |

https://feldfrei.wordpress.com/2014/01/05/funny-statistics/

January 6, 2014 at 3:14 am |

And even if you are little-endian instead of big-endian, 1001001 is still 73, because 1001001 is a palindrome.

July 16, 2014 at 10:03 am |

How many times is “Sheldon’s best number” (73) displayed in binary on the title page of the current Max Planck Research magazine? http://www.mpg.de/8252346/MPR_2014_2

October 2, 2015 at 3:07 pm |

[…] beste Zahl (73, siehe hier) […]

May 30, 2016 at 5:50 pm |

And the best: in morse code 73 is also a palindrome: –……–

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