this post was submitted on 03 Sep 2025
447 points (99.3% liked)

xkcd

13018 readers
33 users here now

A community for a webcomic of romance, sarcasm, math, and language.

founded 2 years ago
MODERATORS
 

xkcd #3137: Cursed Number

Title text:

Another group of mathematicians is working to put an upper bound on the number, although everyone keeps begging them to stop.

Transcript:

Transcript will show once it’s been added to explainxkcd.com

Source: https://xkcd.com/3137/

explainxkcd for #3137

top 27 comments
sorted by: hot top controversial new old

print(uuid())

[–] palordrolap@fedia.io 30 points 1 week ago (2 children)

Felt like noodling a little with some numbers. I have a nice candidate. 22301. Pretty small, right? ~~It's prime.~~ That's not troubling to most anyone's sanity. Edit: one should check one's silly code more carefully before madly pretending to be mad on the Internet. It is not prime. But the intermediate numbers still are.

There's something that can be done to that number four times (but no more) which results in a prime each time and the fourth step results in a 70 digit number that I may have looked at slightly tOo LoNnNg.

Edit 2: Attempt at redemption for the math if not the joke: Start with 5497949 which is prime, and you can do the thing four times and get a prime each time. The last one has 108 digits and, no word of a lie, starts 6969...

Imaginary bonus points for guessing what the heck the operation / something is.b

[–] Audalin@lemmy.world 23 points 1 week ago (1 children)

But 22301 isn't prime? It's 29*769.

[–] palordrolap@fedia.io 33 points 1 week ago (1 children)

Well, this is embarrassing. This is what I get for mathing after midnight.

[–] porl@lemmy.world 9 points 1 week ago (1 children)

The true number messed you up so much you can't recall it any more.

[–] scathliath@lemmy.dbzer0.com 2 points 1 week ago

Can confirm, it stole my lunch money when I tried to see it, then gaslit me and told me my fiancee did. Truly a cursed number.

[–] jaupsinluggies@feddit.uk 8 points 1 week ago (1 children)

If you divide it by itself and add one, you can do that infinitely many times and get a prime every time. Works for all the primes.

[–] sga@piefed.social 1 points 1 week ago* (last edited 1 week ago)

it also works for all perfect numbers (by definition non prime), and also triangle numbers (all triangle numbers greater than 3 or non prime), and also for all numbers above 42, and below 69. quite a neat property sir.

[–] four@lemmy.zip 25 points 1 week ago (1 children)

A moment of silence for all those who sacrificed themselves in the name of science

[–] ZoteTheMighty@lemmy.zip 10 points 1 week ago

Actually, this isn't useful, so we still let it be called "math".

[–] IndustryStandard@lemmy.world 13 points 1 week ago (2 children)

The cursed number is pi. Everyone who tries to fully read it dies. This is why we shortened it to 3.14.

[–] UnrepententProcrastinator@lemmy.ca 4 points 1 week ago (2 children)
[–] whoisearth@lemmy.ca 4 points 1 week ago

Meh close enoigh

[–] Cocodapuf@lemmy.world 2 points 1 week ago

I like 22/7

[–] sga@piefed.social 3 points 1 week ago

everyone who has ever heard of pi, has either died, or will die. just thought of pi gives you a chronic illness which can not be cured

[–] DarkCloud@lemmy.world 8 points 1 week ago

Sounds like those stupid Rationalist cult groups who spend their time coming up with AI fantasies, and claim some thought-experiments are so powerful they'll ruin your mind - real immature stuff. Deserves to be lampooned like this.

[–] ripcord@lemmy.world 6 points 1 week ago (1 children)

Sounds like the seed of an SCP.

[–] Swedneck@discuss.tchncs.de 1 points 1 week ago

peep the horror

[–] nialv7@lemmy.world 6 points 1 week ago (1 children)

If a number is long enough human won't be able to perceive it all at once, so in fact there are only finite number of cases we need to check.

[–] Jankatarch@lemmy.world 3 points 1 week ago

Human will run out of memory when reading the number, in fact.

[–] Dasus@lemmy.world 4 points 1 week ago

Sure there's quite a lot of them to choose from, but for instance USPS tracking numbers are 22-digit numbers.

[–] tisktisk@piefed.social 4 points 1 week ago (3 children)

I'm confused, what is this new lower bound specifically?

[–] finalarbiter@lemmy.dbzer0.com 6 points 1 week ago

The number that makes people go insane is bigger than 2.6*10^21^, or 2,600,000,000,000,000,000,000

[–] pressanykeynow@lemmy.world 4 points 1 week ago

Works as intended then.

[–] ksigley@lemmy.world 3 points 1 week ago

There really is an xkcd for everything.

[–] ShinkanTrain@lemmy.ml 2 points 1 week ago

This is why they invented notation. Just to be safe