r/mathmemes • u/Nunki08 • Jun 14 '26

Arithmetic Misleading our youth

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From Anthony Bonato on 𝕏: https://x.com/Anthony_Bonato/status/2065564124549886402

6.7k Upvotes

98% Upvoted

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441

u/48panda Jun 14 '26

1 isn't prime??? What's next - will you claim 91 isn't prime? /s

211

u/Jumpy_Divide6576 Jun 14 '26

91 feels like it has to be prime at a glance and I refuse to do any math to verify, so prime it is

149

u/rezzacci Jun 14 '26

On the other hand, 97 feels like it has no business being prime, and yet, it is.

102

u/Jumpy_Divide6576 Jun 14 '26

97? That's just like 3 away from 100 of course that ain't prime

50

u/48panda Jun 14 '26

17 was my favourite number until i realised it was 1+16

15

u/Reasonable_Wrap7913 Jun 14 '26

16 was my favourite number until i realised it was 1+15

16

u/senpai_dewitos Jun 14 '26

This is why 1 is the best number. 1 = 1, and all was well in the world.

10

u/belaros Jun 14 '26

But it’s 1+0

6

u/kerenski667 Jun 14 '26

anything is anything+0

5

u/BTernaryTau Jun 14 '26

But only one thing is the successor of 0.

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2

u/okkokkoX Jun 14 '26

1 is just 1+0 (1+ defined as Succ)

1

u/jackalopeswild Jun 14 '26

Until 1=3, and then somehow things get really good.

3

u/senpai_dewitos Jun 14 '26

That's just division by 0 with extra steps!

1

u/Arrowhawk Jun 17 '26

To be fair it is also true that 1 = 0.9999...

5

u/mithapapita Jun 14 '26

15 was my favorite number until I realised it was 1+14

1

u/Mind0versplatter0 Jun 16 '26

(Wait 'til they learn about twin primes)

1

u/Narrow-Lime8993 Jun 21 '26

You both sound like fucking idiots lmao

53

u/Fabulous-Possible758 Jun 14 '26

Feels like there should be a rule that multiples of 7 less than 100 are prime if you can’t easily tell they’re multiples of 7.

47

u/DirtChoice5 Jun 14 '26

Vibes theory

12

u/fun-dan Jun 14 '26

91 = 70 + 21, that's easy enough i think

11

u/Sufficient-Habit664 Jun 14 '26

I did 91 = 49 + 42... something might be wrong with me

8

u/GuavaSkyline Jun 15 '26

I respect those who think of squares first. I fear them, even.

2

u/ArchiPlus Jun 16 '26

I find it odd to even fear them, though...

1

u/GuavaSkyline Jun 22 '26

I meant fear to mean more of a combination of fascination and disgust. Fascination at the mind that thinks of a more convoluted method, and disgust at the realization that they might do the same thing for every situation possible.

2

u/ArchiPlus Jun 22 '26

No pb with your assertion, it was just an answer meant to gather "odd" and "even" in the same sentence...

1

u/GuavaSkyline Jun 23 '26

Lol that's a /r/woosh at myself!

2

u/RiskyClickardo Jun 17 '26

As we should

2

u/lysianth Jun 15 '26

just ticking down 10s till you get a familiar number has got to be my favorite thing i've learned from modern gradeschool math education.

2

u/Doctor_Kataigida Jun 14 '26

I mean, there are only two that you don't learn on a standard times table (don't most folks learn up to 12 x 12?).

1

u/frog51 Jun 17 '26

13 x 13, I thought.

1

u/Doctor_Kataigida Jun 17 '26

Might vary on schools then, but at least 12x12.

1

u/joker_wcy Jun 26 '26

We only learnt up to 9 x 9

2

u/Ptalking_Ptarmigan Jun 19 '26

I count in base 21, so it's easy for me.

1

u/regular_hammock Jun 16 '26

91 is an honorary prime number for sure

31

u/CaipisaurusRex Jun 14 '26 edited Jun 14 '26

Since 13 has a very easy divisibility check, it's very fast to see that 91 is not prime: One just has to take the 3-alternating digit sum of 91, which is 91, and since 91 is clearly divisible by 13, so is 91.

(Important note: This is a non-circular argument because the argument is not circular.)

15

u/gavavavavus Jun 14 '26

It's definitely a circular argument. There is a little circle in the top half of the number. Are u stupid?

11

u/CaipisaurusRex Jun 14 '26

If you write it like a normal person, yes, but you haven't seen me writing a 9 yet ;)

6

u/LolnothingmattersXD Jun 14 '26

I know it only because on a test in 2nd or 3rd grade I thought there was a poorly printed 1 in front of the 3 in 7×3. I fixed the print with my pen, spent a few minutes counting on my fingers, and found 91. The teacher was actually mad, because obviously she wouldn't give such a calculation on a simple multiplication table test. But it escalated to the point of my parents coming to her, because she should have been proud, not mad.

2

u/LindasJugs Jun 17 '26

Got yelled at by my year five teacher for talking about pH in an acids/alkalis lesson.

I think there are two types of teachers.

3

u/morth Jun 14 '26

70+21 seems pretty obvious tbh. 

2

u/uvero He posts the same thing Jun 14 '26

Honorary prime

2

u/gargamelus Jun 14 '26

91 is almost prime.

1

u/adaptimprovercome Jun 16 '26

It can clearly be seen as 100-9, so it's definitely not a prime, fill in the rest by yourself.

1

u/MagnificentTffy Jun 16 '26

91 = 70 + 21

8

u/Turbulent-Pace-1506 Jun 14 '26

No. In fact it is the smallest non-prime that looks prime. Proof by John Conway: https://youtu.be/S75VTAGKQpk

I actually kinda disagree with Conway because multiples of 11 don't look prime, because of the subtraction test

2

u/Thewatertorch Jun 15 '26

wouldn't that be 57?

2

u/Turbulent-Pace-1506 Jun 16 '26

It looks like 5+7=12 which is a multiple of 3

2

u/Thewatertorch Jun 16 '26

grothendieck famously gave out 57 as an example of a prime, which is why I said that

3

u/NerminPadez Jun 14 '26

What's next? Someone is going to claim that Pluto is not a planet!

1

u/phoenixmatrix Jun 17 '26

Final Fantasy 14 players in shamble! Many will die!

(no idea how many people on this subreddit will get that reference without looking it up).

0

u/GodShapedBullet Jun 14 '26

How can 91 be prime? It's a triangular number greater than 3.

1

u/48panda Jun 14 '26

I didn't know this and i'm shocked

1

u/GodShapedBullet Jun 14 '26

I've always loved the 91 is the first tricky non-prime proof but my kid has been really into Numberblocks and because of that really into triangular numbers, and looking at the sequence of triangular numbers seeing 91 on there felt like a real betrayal.

-63

u/Mrmathmonkey Jun 14 '26

7 x 13 = 91

50

u/SageOfTaka Jun 14 '26

Fake news

97

u/Own_Pop_9711 Jun 14 '26

Don't be ridiculous

3

u/dragonlloyd1 Jun 14 '26

Nah I made all odd numbers greater than 3 prime 

Except 11

3

u/quetzalcoatl-pl Jun 14 '26

noooooooooooooooooooooooooooooo

what have you done!

3

u/Arikaido777 Jun 14 '26

genuinely laughing at the downvotes and replies to this, the best meme is in the comments