Is 73+47 Really Equal to 5? The Answer May Surprise You!

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Discussion Overview

The discussion centers around the claim that 73 + 47 equals 5, exploring the implications and interpretations of this statement, particularly in relation to factorial notation. Participants engage in a mix of humor, mathematical reasoning, and critiques of the original claim, examining its significance and the nature of mathematical communication.

Discussion Character

  • Debate/contested
  • Exploratory
  • Mathematical reasoning
  • Conceptual clarification

Main Points Raised

  • One participant asserts that 73 + 47 = 5 through calculations, inviting challenges to this claim.
  • Others question the significance of the claim, asking for clarification on its relevance.
  • Some participants note that the equality is related to factorials, specifically that 5! equals 120, which is the sum of 73 and 47.
  • Discussion includes the observation that both 73 and 47 are prime numbers and that their difference has interesting mathematical properties.
  • Participants express skepticism about the original claim and the intent behind it, with some suggesting it may be a riddle or joke.
  • There are critiques of the communication style, with some participants feeling that the joke relies on an elitist understanding of mathematical notation.
  • Several participants engage in a meta-discussion about the appropriateness of the thread's placement and the nature of humor in mathematical contexts.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the validity or significance of the original claim. There are competing views on the interpretation of the factorial notation and the appropriateness of the joke, leading to a mix of agreement and disagreement throughout the discussion.

Contextual Notes

Some participants express confusion over the use of factorial notation and its implications, while others highlight the potential for misunderstanding among those unfamiliar with mathematical conventions. The discussion also touches on the cultural context of mathematical humor.

Archosaur
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Guess what! Through complete and precise calculations, I have discovered that 73+47=5! Isn't that crazy? I stand firm by my conclusion and beseech anyone to challenge me!

I'm actually serious, by the way. I know how some of you might take this, but I'm not lying.

I would bet my life on the truthfulness of that equality.
 
Mathematics news on Phys.org
I'm not going to check your calculation right now but if it is true then why is it significant?
 
Archosaur said:
I would bet my life on the truthfulness of that equality.

Well of course it's true... but, what is the point of your thread?
 
Even better, did you know that 2=2!
I think that is pretty amazing..
 
cristo said:
Well of course it's true... but, what is the point of your thread?

For a few seconds there I had to think about this also... The equality isn't simple enough at first glance to be another one of "those" threads.
 
Mentallic said:
For a few seconds there I had to think about this also... The equality isn't simple enough at first glance to be another one of "those" threads.
What is not simple? Pick any integer, take its factorial and you can always find two numbers that add up to it.

Archosaur, it is also true that 55+ 65= 5! or the 23+ 97= 5!. What is special about 73 and 47?
 
HallsofIvy said:
What is not simple? Pick any integer, take its factorial and you can always find two numbers that add up to it.

Archosaur, it is also true that 55+ 65= 5! or the 23+ 97= 5!. What is special about 73 and 47?

You really are uninsightful today, Halls!

First off, 73 and 47 are PRIMES, but even more amazing, their difference is the only integer that is squeezed in between a cube and a square, as Ramanujan proved!
 
HallsofIvy said:
What is not simple? Pick any integer, take its factorial and you can always find two numbers that add up to it.

Archosaur, it is also true that 55+ 65= 5! or the 23+ 97= 5!. What is special about 73 and 47?

arildno (post#4) has given us a special equality, which happens to be very simple. (I wouldn't stop twice to think about its elegance).

Arildno, if this equality has some special features as you have stated, please explain in a little more detail what 'an integer squeezed between a square and a cube' means :smile:
 
25= 5 squared; 27=3 cubed. so the difference between them is one less than a cube and one more than a square.
Is it really that amazing that they're both primes? Goldbach's conjecture has been numerically verified for every number up to the order of 10^18 (according to wikipedia!). 5! is an even number...
 
  • #10
I have just checked "the penguin dictionary of curious and interesting numbers author David Wells" and 120 appears there.It is the 15th triangular number the 8th tetrahedral number,the list goes on.
 
  • #11
Okay okay okay, so you knew the trick right away...

I knew I should have posted this in the physics section...

See? You were supposed to think that I was just exclaiming that 73+47=5, but you all immediately identified the factorial. I'll go find some history majors to try it on.

And yes, 73 and 47 are special, kinda. Firstly, they were the first prime numbers that came to my head that add to 120, but then I noticed that they are the 20th and 15th primes, respectively and 20-15 is 5, which is the number that I took the factorial of.

Anyway, sorry for the attempted deception :)
 
  • #12
Archosaur said:
Okay okay okay, so you knew the trick right away...

I knew I should have posted this in the physics section...

No.. you should have posted this in the general discussion section, or better still not posted it at all. :rolleyes:
 
  • #13
Archosaur said:
Okay okay okay, so you knew the trick right away...

I knew I should have posted this in the physics section...

See? You were supposed to think that I was just exclaiming that 73+47=5, but you all immediately identified the factorial. I'll go find some history majors to try it on.

And yes, 73 and 47 are special, kinda. Firstly, they were the first prime numbers that came to my head that add to 120, but then I noticed that they are the 20th and 15th primes, respectively and 20-15 is 5, which is the number that I took the factorial of.

Anyway, sorry for the attempted deception :)

You should try it on forums devoted to social "sciences", or for nurses, or for primary school teachers and suchlike. I'm sure there will be much flutter and chatter over your problem in such places.
 
  • #14
If the postfix factorial notation is not interpreted as a punctuation mark then your sentence is a grammatical failure. It would be nice if you could sneak some punctuation into the original joke to overcome this flaw.
 
  • #15
Archosaur said:
See? You were supposed to think that I was just exclaiming that 73+47=5, but you all immediately identified the factorial. I'll go find some history majors to try it on.

Why? To give a brilliant demonstration of smart-assedness?

The fact that you know "!" can be interpreted as a mathematical operator doesn't make you smarter than those who don't. Which is pretty obvious given that very few would be impressed by remarking that "73+47=120" or "73+47=2*3*4*5"
 
  • #16
alxm said:
The fact that you know "!" can be interpreted as a mathematical operator doesn't make you smarter than those who don't.

(1) The exclamation point for factorials has been used for over 200 years, and in the US it is generally taught in middle school.

(2) There are dozens of riddles of this type that have to do with obscure meanings of words, whereas "!" for factorial is the secondary usage that most pople will think of if pressed.
 
  • #17
confinement said:
If the postfix factorial notation is not interpreted as a punctuation mark then your sentence is a grammatical failure. It would be nice if you could sneak some punctuation into the original joke to overcome this flaw.

Haha, yes I did notice that. I thought about sneaking a period in after the "!", but that would make it even more obvious... Oh, I could write "...73+47=5!" and say that it's "73+47=5*4*3*2" and "!" which is still grammatically incorrect, but maybe it's closer.


alxm said:
Why? To give a brilliant demonstration of smart-assedness?

The fact that you know "!" can be interpreted as a mathematical operator doesn't make you smarter than those who don't. Which is pretty obvious given that very few would be impressed by remarking that "73+47=120" or "73+47=2*3*4*5"

Whoa dude. I'm just playing around. Of course that doesn't make me smarter and I never said it did. No need to go on the defensive. Lighten up a little.
 
  • #18
cristo said:
No.. you should have posted this in the general discussion section, or better still not posted it at all. :rolleyes:

at least you were nice about it...
 
  • #19
  • #20
you guys need to do a better job at spotting trolls when you see them
 
  • #21
confinement said:
(1) The exclamation point for factorials has been used for over 200 years, and in the US it is generally taught in middle school.

And promptly forgotten. Most people don't know it or need to know it.

(2) There are dozens of riddles of this type that have to do with obscure meanings of words

So there are lots of stupid 'riddles'. And?
 
  • #22
Archosaur said:
Whoa dude. I'm just playing around. Of course that doesn't make me smarter and I never said it did. No need to go on the defensive. Lighten up a little.

No, but you made a lame joke, where the 'punchline' amounts to "Ha-ha, you don't know what a factorial sign is." and then implied you'd have more fun telling it to 'history majors'. I'm just telling you that that would be usually perceived as assholeish, elitist, behavior. Same goes for a history student trying to stump a physicist with an obscure history reference.
 
  • #23
qntty said:
http://mathworld.wolfram.com/Multifactorial.html

A lot of people would find that confusing because I would have thought ! would mean to apply the factorial operator twice. Post that on a computer science form and you'll stump a lot of people.
 

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